Bumblebee Jasper

Honey bee Jasper is a deceptive name of calcite (calcium cabonate) with considerations of arsenic and manganese oxides with banding and layering which is looks like a honey bee that why it called honey bee Jasper.

 

The inclusions caused by sulfur (yellow), calcium & Aragonite (white), Orpiment & Realgar (orange), and Pyrite (black).

bumblebee Jasper (Calcite)

This mineral was only discovered in the 1990’s  west Java Province, Papandayan Volcano, Indonesia. Since then, this mineral has yet to be discovered anywhere else on Earth and geologists don’t expect to find another deposit of it anytime soon. This is an extremely rare occurrence in nature that simply doesn’t happen and it should be cherished, respected, and valued for the true uniqueness it holds.

The Dichroscope, it types, its construction and its uses

T

he dichroscope is a pocket-sized tool that can aid in the identification of gemstones. This tool is used to inspect pleochroism (leochroism is the change of color in colored anisotropic double refractive  gemstones when viewed from different directions) in gemstones and to quickly separate some common stones from each other (such as ruby versus red garnet).

Basic

There are two types of dichroscopes on the market:

• calcite dichroscopes
• polarizing dichroscopes

In anisotropic gemstones, different colors are absorbed in different directions ("directional selective absorption") which causes the pleochroism that is observed with the dichroscope.

Calcite dichroscope

The calcite dichroscope is the preferred type of dichroscope used in gemology. It works because the calcite rhomb (Iceland spar) separates the polarized slow and fast ray emerging from the gemstone. If you look at the viewing end of the dichroscope, two small windows are seen.
A gemstone is placed in front of the aperture (slightly touching it) with a strong white light source (such as a penlight) directly behind the stone. Light enters through the aperture of the dichroscope. The pleochroism colors inside the gemstone are separated by the calcite rhomb. The glass prisms on either side of the rhomb are there to guide the light straight through the instrument.

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Calcite dichroscope

Calcite Dichroscope 

Calcite Dichroscope 

view in calcite dichrosoope 

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Polarization dichroscope

Two polarizers

Pleochroism may also be observed with the use of a polarizing filter. The disadvantage is that one will only see one of the pleochroic colors at a time, making subtle changes of colors (shades) difficult to recognize. This can be overcome by placing two polarizing filters close together, each orientated 90° to the other (one in North-South and the other in East-West position).

Although this kind of dichroscope is very economical, the results obtained by them are less clear than in the calcite ones. Stones with weak pleochroism will be hard to determine with this type of tool.

The London dichroscope is a popular brand.

Polarization dichroscope

pleochroism in polarization dichroscope

pleochroic stone in london dichroscope 

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Proper use and possible observations

Inspection directions

1. through the table
2. through the crown facets
3. another direction through the crown facets
4. through the girdle
5. a different direction through the girdle

There are three possibilities to test the gemstone in Dichroscope

1. the colors in both windows remain the same in all directions

the stone is isotropic (single refractive)

2. in total 2 colors are observed  

the stone is anisotropic uniaxial

3. in total 3 colors are seen

the stone is anisotropic biaxial

Pleochroism in different gemstones 

Pearl and different types of pearls

Pearl (Indian: Moti; Italian: Perla) is classified into two basic category – Natural and Cultured. The term synthetic must not be used with respect to pearls. Materials which simulate or look like pearls, but do not have either the composition or structure, are known as imitation pearls.

• Natural Pearl
  • Saltwater Pearl
    • Persian Gulf
    • Australia
    • Japan
    • Straits of Manaar (Region between India & Sri Lanka)
    • South Sea Islands
  • Freshwater Pearl
    • Mississippi (U.S.A.)
    • China
• Cultured Pearl
  • Saltwater Pearl
    • Japan
    • Australia
    • Philippines
    • South Sea Islands
  • Freshwater Pearl
    • Lake Biwa (Japan)
    • China
• Imitation Pearl are products, completely or partially man-made, imitating the appearance, colour and effect of natural or cultured pearls without possessing the physical and chemical properties, even when using natural substances.

Information on Pearls

Pearls are produce by molluscs which are saltwater oysters and freshwater mussels.

The oyster consists of a soft visceral mass enclosed between two halves of the shell which are hinged together. Like every other animal, an oyster possesses a heart, stomach and mouth. It breathes through its gills and feeds itself with micro-organisms and planktons in the water.

• Pearl Oysters belong to the Pinctada family of the mollusc group in class Lamellibranchia. Pinctada molluscs are saltwater oysters. Molluscs like Unio and Hyriopsis are freshwater mussels.
• The shell is composed of various layers.
• The first layer is dark horny outside layer composed of organic substance conchiolin, a protein like substance.
• It is also the binding agent that holds the aragonite crystals together.
• The inner layer is a thicker crystalline layer of prismatic calcium carbonate in the form of calcite.
• Mother of Pearl is the smooth pearly lining (layer) on the interior of a mollusc shell. It is composed of CaCO₃ as aragonite crystals and a little water and conchiolin.
• Aragonite layer is made up of microscopic platy calcium carbonate crystals arranged in an overlapping manner.
• Nacre is a protective pearly substance secreted by the mollusc and deposited around an irritant, in layers. These layers decide the lustre and quality of a pearl. The thinner the layer, the better is the lustre and vice versa.
• Mantle is a fold of epithelial material that envelopes the internal organs of the animal and is situated at the meeting point of the inner sides of the shell. It secretes conchiolin, aragonite and calcite.
• Orient of a pearl results from the diffraction of the light through the aragonite crystals.
• When white light is reflected from two different surfaces very close together, the two reflected waves can be out of phase, which causes interference, resulting in rainbow colours.
• The finer the pearly layers, the greater the orient that the pearl will possess.

Pearls Produced by Snails

• Abalone Pearls: Found off the coast of New Zealand, California, Mexico, Japan and Korea. These pearls are known for their almost opal like appearance. The colours may be any combination of green, blue, pink or yellow and usually have an irregular shape.
• Conch Pearl: These pearls are found in the great Conch, a large marine snail found throughout the Caribbean. Commonly pink, white or brownish. They are also called ‘pink pearls’ and may have distinctive flame like surface markings. These pearls do not have a nacreous coating and appear more as corals.
• Comparing a pearl and a ball of mother-of-pearl, it will be seen that the pearl has lustre over its entire surface, whereas the ball of mother-of-pearl has this in only two places. This is because their structures are totally different.
• The mother-of-pearl has relatively flat layers, whereas the pearl has been formed around a nucleus in concentric layers.
• The components of pearls or mother of pearl are affected by the food, the salinity, the water temperature and the region where the oyster-beds are found.

Composition                       Pearl                Mother of Pearl
Calcium Carbonate (Aragonite)19.72%           84.75%
Organic Material (Conchiolin)    5.94%            11.76%
Water                                         2.23%             3.17%
Other Substances                   0.11%                 0.50%  Chemical Composition : Calcium carbonate, organic material and water Classification / Type :  On the basis of shape, body color, overtone and source. Crystal System / Forms :  None. Partially crystalline and partially amorphous. Cuts & Uses :  As cabochons, beads, carving, etc. Dispersion : None. Hardness : 2.5 - 3.5 Lustre : Varies from almost dull to a near metallic in black pearls; orient may be sheen. Magnification :  Drill hole might show the layered internal structure, presence of dye. More Information : Pearl Treatments Skinning: It is performed by removing a bad coloured or blemished outer layer, so that a more attractive, although smaller, pearl could be obtained. The layer is removed by careful filing or by the use of abrasive emery paper. Soaking: Cracks in the surface of pearls are sometimes cured by soaking them in warm olive oil. Coloured Impregnation (Dyeing): Staining is commonly done on Akoya pearls. The pearls are soaked in a weak solution of silver nitrate and dilute ammonia and then exposed to light or hydrogen sulphide gas. Occasionally the core (bead nuclei) is dyed before they are inserted in the oyster to produce a different overall colour. It is performed on white pearls to change them into black pearls. Coating: Pearls may be coated with any pigment to give different colours. Bleaching: Removal of a secondary colour or stains from the deposit of organic matter. This is done by immersing the pearls in a solution of oxygenated water and afterwards exposing them to light. Irradiation: Some pearls are darkened by treating them with gamma rays. Commonly Akoya pearls are treated to various coloured shades. X-rays may give a reduced silver shade. Most pearl enhancements are difficult to detect with conventional equipment. Enhancements such as skinning and bleaching are often considered as part of the processing of pearls by traders. Optic Character :  A.G.G. Pleochroism : None. Refractive Index / Birefringence :  1.530 – 1.686 (Spot reading: 1.55) / 0.156 Simulants (with separation tests) : Cultured pearl (structure) Imitation pearl (surface pattern) Sources :  Persian Gulf, India, Sri Lanka, Philippines, Malaysia, Australia, Tahiti, Mexico, Panama, Venezuela etc. Specific Tests : Drill hole test; candling X-ray diffraction / radiography Endoscopy Lucidoscope      Spectrum :  None. Synthesis :  None.

Natural Pearl and its identification

Natural Pearls are organic gemstone formed inside a pearl oyster due to the concentric deposition of nacreous layers around any foreign body which has entered the animal accidentally, without the aid of any human agency.

How are natural pearls formed?

It is the result of an accident.

• A fish searching for food passes near an oyster and finding nothing moves off elsewhere by using its tail.
• This movement causes a cloud of sand, from which several grains lodge in the oyster.
• The oyster can get rid of most of these, except those which bury themselves in its flesh.
• These, along with a few epithelial cells will be changed into pearls.
• In a pearl, only aragonite is formed, in concentric layers.
• The aragonite crystals have their optic axes at right angles to their main surfaces, so that all the optic axes in a pearl are radial.
• This is important not only in the creation of the pearl’s lustre and orient but in determining the differences between a natural and a cultured pearl.
• The aragonite layers are not continuous, but have irregular edges where a layer is not complete.
• This is the cause of the roughness of a natural or cultured pearl when rubbed against the teeth, compared with the smoothness of an imitation pearl.
• Depending on the parasites which attack them, and the way in which they react, various pearl formations are produced.
• Among these are found Baroque pearls, Blister pearls and Concretions.
• Salt water and fresh water oysters and mussels can produce nucleated and non nucleated pearls.
• Blister Pearls are swellings which are formed on the inner surface of the oyster shell or mussel.
• They must be removed very carefully from the shell so that the layer of mother-of-pearl remains.
• In some cases, when cut from the shell, the base remains flat and without a pearly coating.
• If they were detached, the pearl might well be too small or too baroque in its shape.
• Baroque Pearls are formed within the mantle and are distorted and irregular in shape. They occasionally resemble familiar objects such as teeth, tadpoles, mushrooms or snails.
• Pearl Concretions are caused by the amalgamation of a number of small natural pearls in the mantle of the oyster. Pearl concretions are always baroque in shape and rarely of much value.

The chemical composition of a pearl can vary according to its place of origin. In certain cases the quantity of organic material or of water percentage is different. But these variations are very minor and the following figures are fairly accurate.

Composition	Natural Pearl
Calcium Carbonate (Aragonite)	91.72%
Organic Material (Conchiolin)	5.94%
Water	2.23%
Other Substances	0.11%

Colour: Pearls are found in many colours. Colour in pearls is defined by:

• Body colour is the predominant basic colour of the pearl.
• Overtone is the one or more colours that overlie the body colour.
• Orient is the play of colour effect observed over the surface. It may be a combination of pink, blue, green and silver shades.

Cause of Colour: The main factors which are responsible for the colour in pearls can be classified with respect to the environment and the chemical and optical properties.

• Environment
  1. Presence of mineral salts and salinity in the water. This is related to the rock types and the associated soil e.g.
     • A small amount of magnesium carbonate, without iron or aluminum gives the white colour.
     • Iron gives a light brown colour.
     • Copper carbonate (azurite) gives a blue colour.
     • Zinc carbonate (smithsonite) gives a grey colour.
     • Cream and gold contain a large percentage of magnesium carbonate, iron oxide and aluminum.
  2. Amount of plankton. Water rich in plankton gives the pearl a light green tint.
  3. Temperature of the water. In general, moderate temperature produces finer lustre in pearls, warmer waters produces duller lustre.
• Chemical and Optical properties: Chemicals include the presence of chromophore (colour causing elements), while the optical effects include the quality of internal reflections and interference of light. As a result colours obtained are pink, white, silver (optical) and yellow, salmon pink, black, blue (chemical).

How to identify natural pearl?

The separation of natural pearl from cultured pearl is not possible without the use of certain distinct testing techniques. With regular improvements in the culturing process it is getting more and more difficult to conclusively identify natural pearls. On the whole, the percentage of natural pearls available is very minimal in comparison to the cultured pearl availability. Most of the following are indicative tests and not conclusive. But when performed together, they provide conclusive evidence.

1. Tooth Test: Rub the pearls lightly along the surface of your upper teeth.
   • If they feel gritty or rough, they may be pearl.
   • Care should be taken since it may scratch the pearls if done improperly.
   • Both natural and cultured pearls often exhibit the same reaction.
   • As such this test can be used to distinguish between Imitation pearls and Natural / cultured pearls.
2. Drill Hole Test: Examine the drill hole area with a magnifying lens.
   • If a dark dividing line separating the nacre from a pearl bead nucleus is visible, the pearl is a cultured pearl.
   • If a series of growth lines, which get more yellow or brown towards the centre, is seen, it is a strong indication of a natural pearl.
   • The diameter of a drill hole can also give some detail about the nature of the pearl.
   • In the case of a cultured pearl, the drill hole measures 0.06mm while in a natural pearl it is rarely larger than 0.04mm.
3. Lucidoscope: This technique uses the fact that the transparency of the layers of nacre (mother-of-pearl) varies depending on the direction from which it is viewed under a strong beam of light.
   • This can be observed with the naked eye or with a lens.
   • A cultured pearl with an MOP nucleus would be more transparent along the parallel layers of the bead nucleus than down the length.
   • This effect is better observed in immersion rather than in air.
   • Commonly pure benzene is used since it evaporates quickly and therefore does not harm the pearl.
   • This technique fails when thick skinned cultured pearls are examined.
4. Pearl Compass: The principle of the instrument is that a certain position according to its crystallographic magnetic field.
   • This instrument consists of powerful magnets, in the centre of which is suspended the pearl to be tested using a torsion free thread.
   • Due to differences in their internal structures, a cultured pearl with a mother-of-pearl core will cause the pearl to turn because of its layered structure.
   • The radial and concentric structure of a natural pearl does not exhibit the turning movement.
5. Endoscope: This instrument consists of a powerful source of light within housing. The light beam is then passed through a fine hollow needle which has an aperture and two polished mirrors at its end aligned in opposite directions at 45° to the beam of light. The light beam travels through the tube and reflects from the first inner mirror through the aperture into the pearl being examined.
   • In the case of a natural pearl, this reflected light enters the concentric layer structure and travels round it by a process of total reflection, until it strikes the second mirror.
   • It is then reflected off this mirror and out through the drill hole where it will be seen as a bright flashes when examined through the microscope.
   • In the case of a cultured pearl due to the layered structure of the nucleus, the light is not reflected onto the second mirror, but instead is transmitted through the parallel layers and is lost to the observer and no flash of light is seen.
6. Lauegrams: A narrow beam of x-rayspassed through pearl exhibits a pattern of spots on a photographic plate.
   • The pearl must be examined in three different directions to obtain an accurate result.
   • Two distinct patterns are observed for natural and cultured pearls.
   • Natural pearls will exhibit a hexagonal spot pattern in all directions.
   • Cultured pearls will exhibit a hexagonal and a tetragonal spot pattern depending on the direction in which they are examined.
7. X-Radiography: This test relates to the transparency of the pearl structure to X-rays.
   • Conchiolin, which is an integral part of the pearl structure, is more opaque to X-rays than calcium carbonate.
   • As a result, a natural pearl will show a concentric structure from the centre to the surface.
   • In a cultured pearl either the central portion is broad (non-nucleated) or with parallel layers surrounded by concentric structures (nucleated).
   • A complete string of pearls can be examined at a single exposure.
8. Fluorescence: In general, natural pearls exposed to X-rays do not exhibit any fluorescence. However, Australian pearls and freshwater pearls have been known to fluoresce. Cultured pearls generally tend to fluoresce under X-rays with the exception of some non-nucleated pearls.

Cultured Pearl and Identification of culture pearl

Cultured pearls are nacreous formations secreted in the interior of productive molluscs. The secretion is started by human intervention and the rest of the process is performed by the molluscs themselves.

Cultured pearls were first licensed in A.D.1907. The names of Mise, Nishikawa and Mikimoto are almost always linked with the history of cultured pearl production. Pearl culturing these days is a highly organized, commercial enterprise which is very quality conscious.

How are cultured pearls made?

Pearl culturing requires the following criteria to be fulfilled to obtain a good yield and quality.

1. Pearl Farm: Factors to be considered are:
   • Temperature of the water should be fairly constant, with little fluctuations.
   • The salinity and the mineral salts must be considered.
   • The type of sea-bed, whether rocky or sandy, and its accessibility.
   • The presence of mild currents is important as they provide the food and oxygen to the oysters.
   • The farming region should be protected from natural climatic hazards.
2. Oyster preparation and requirements:
   • The oysters are starved for several days to ensure that they can be opened much more easily, their gonads emptied and that the risk of rejection of the nucleus is reduced.
   • Cores which are used as the nucleus are made from the shells of freshwater mussels (mainly those from the Mississippi). Their specific gravity is similar to that of a pearl and they have a neutral white colour. The shell is cut into thin sheets, then cubes, which are rounded in a tumbler. Diameters can vary as per the demand.
   • Grafts: A graft is a small piece of the mantle which contains the cells producing the mother-of-pearl or nacre. This is inserted along with the nucleus and is responsible for the formation of the pearl. A strip is cut from the edge of the mantle and is carefully cleaned. The size of each graft should be such that it covers about one third of the core. A graft can live for about two hours in contact with seawater and should be utilized almost immediately.
   • Operating Theatre: Since the entire process is similar to a major operation, care should be taken to maintain hygienic conditions and well trained staff so as to control and prevent the death of oysters.
3. Culturing Process: This involves the following stages and can vary slightly for the production of round pearls and mabe pearls.
   • The oyster is carefully opened with a sharp knife and held open by placing a wooden chock between the shells.
   • The gonad or the reproductive system is the organ in which the implant of the graft and core is best tolerated by the oyster and produces the best results. This produces round pearls.
   • The graft and the core are inserted into the gonads to the required position.
   • Mabe pearls are produced by inserting a dome – shaped nucleus of mother of pearl, between the mantle and the shell of the oyster.
   • During a single operation, two cores can be implanted at the same time.
   • The oysters are then returned to the sea for a period of two to three years or until sufficient nacreous coatings have been deposited.
   • The pearl is then extracted from the pearl sac. In some cases, another core is inserted and the oyster returned to the sea.
   • In the case of mabe pearls, it is cut from the shell, cleaned and the hollow hemisphere is filled with a polyester resin and then closed with a mother of pearl backing.
   • Harvesting is done during the winter season when the layers deposited are finer and with a better lustre. Once the harvest is over the pearls are processed to remove any organic impurities. The pearls are slightly bleached, which on drying gives a whiter appearance without the green tinge that freshly collected pearls always have.
   • The pearls are now sortedon the basis of shape, colour, orient and size.
     • Shape plays a major role in determining the price of pearls. Pearls can be generally considered under the following categories:
       • Round
       • Seed pearls (very small rounds)
       • Slightly flattened round
       • Baroque (irregular, pear shaped etc.)
     • Colour is defined by the body colour, overtone and orient, e.g. a white body colour with a pink overtone known as rose, or a silvery or white overtone, a natural black or steel gray body colour with good orient is fairly highly priced.
     • Orient should be judged using a standard daylight lamp against a dead white background.
     • Size is measured in terms of weight and diameter, e.g.
       • 1 carat = 4 pearl grains
       • 1 momme = 18.75 carats
     • Drilling of pearls: A pearl may be half drilled or completely drilled as per the requirement. Drilling is commonly done using a hand drill.

Types of Cultured Pearls

In trading circles a number of different terms are used to define pearls from specific locations or those of a particular type. The following are a few of the terms.

• Akoya Pearl: Saltwater pearls from the Akoya Oyster (pinctada fucata martensii). These are usually cultured, round, and their natural colours are pink, white, and yellowish.
• South Sea Pearls: This refers to large white pearls cultured in the pinctada maxima oyster – a large oyster found in the South Seas. There are two types of oyster called the silver-lip or gold-lip depending on the colour of the lip of the shell. Commonly found in the salt water area extending from Myanmar and Indonesia, down to Australia and across to French Polynesia.
• Black Pearl: These are grey to black coloured cultured pearls. Cultivated in the South Pacific from the black-lip oyster, pinctada margaritifera. The colour is an inherent characteristic of the pearl nacre. These are naturally black and not those that have been dyed.
• Biwa Pearl: These are freshwater cultured pearls cultivated in Lake Biwa, Japan’s largest lake. Nucleated and non-nucleated pearls are cultured here.
• Mabe Pearl: In the manufacture of a mabe a half-bead, dome-shaped nucleus (often of plastic or soap stone) is stuck on the inner surface of the shell. Once the nacre is secreted over the bead, the blister pearl is cleaned to prevent deterioration. The hollow shaped base is then filled with a paste, wax or resin and covered with a mother-of-pearl backing. The term blister mabe is also used.
• Mikimoto Pearl: Pearls produced and marketed by the Mikimoto Co. They are known for having a higher lustre and fewer flaws than the average Akoya pearl.
• Half Pearl: A whole pearl that has been ground or sawed on one side, usually to remove blemishes. If about 3/4 of the pearl remains it is called a half pearl. The term half pearl is also used to refer to blister pearls.
• Blister Pearl: Natural or cultured pearls that grow attached to the inner surface of the oyster or mussel shell, and when cut from the shell, one side is left flat with no pearly coating.
• Keshi Pearl: Naturally occurring very small, round / baroque, non-nucleated pearls, which form accidentally as a by – product during pearl formation (natural or cultured). Keshi is the Japanese word for poppy seed.

Minerals / Gemstones crystal Systems

 

Crystal Structure

The crystal structure of a gem material determines how the gemstone absorbs light. Crystal shape may also influence the shape of a finished gemstone: most gemstones are cut to maximize the yield from the rough stone. Familiarization with crystal systems will give you more insight about why gemstones each have unique properties. Most gem materials are formed when a mineral crystallizes deep in the earth. The shape of the crystal is a function of the mineral's chemical formula and the way the atoms are bonded together and arranged in a precise pattern. Generally transparent gemstones have been cut from a crystal. There are seven basic crystal systems:

• Cubic
• Tetragonal
• Orthorhombic
• Monoclinic
• Triclinic
• Hexagonal
• Trigonal

 

Isometric System (Cubic System)

The isometric system is comprised of three equal length axes that are all at right angles to each other. This system is also called the cubic system. Think of a cube of sugar. Gemstones that crystallize in the cubic system include diamond, garnet, spinel and fluorite.

Cubic system

Diamond

Diamond is a transparent gemstone composed of carbon atoms arranged in a crystal lattice structure. Diamond is the hardest mineral on the Mohs scale with a rating of 10.

Natural and synthetic diamond crystal shape 

Garnet

Garnet is a group of minerals that have been used since the Bronze Age as gemstones and abrasives. Garnets possess similar physical properties and crystal forms, but differ in chemical composition.

Spinel

Spinel is a magnesium aluminum oxide mineral that occurs as octahedral crystals, flattened crystals, and twins. Spinel is often found in ruby and sapphire deposits.

Fluorite

Fluorite is a halide mineral composed of calcium and fluorine. Fluorite occurs in a variety of colors, including purple, green, yellow, blue, and white. The purple and green colors of fluorite are the most popular for gemstones.

Tetragonal System
The tetragonal system has three axes that all intersect at right angles; but two are equal in length and the third can be longer or shorter. Zircons  crystallize in the tetragonal system.

 

 

 

 

Hexagonal System
The hexagonal system has four axes; the three axes on the horizontal plane intersect at 60^o angles. The fourth axis intersects the horizontal plane at right angles. Gem material with the hexagonal crystal shape are easily identifiable crystals with six-fold symmetry. Gemstone materials that form in the hexagonal system include: corundum, Beryl, Tourmaline and Quartz .

 

Hexagonal System 

Trigonal System

Some minerals of the hexagonal system form with a three fold symmetry rather than six; these can be called "trigonal"; but the trigonal system is a subgroup of the hexagonal system.

 

 

Orthorhombic System
The orthorhombic system has all three axes at right angles, but all axes are a different length. Gemstones that crystallize in orthorhombic crystals include Topaz, Peridot, Andalusite and Chrysoberyl 

 

Orthorombic System 

Monoclinic System
The monoclinic system has two axes at right angles and one that is not perpendicular. All axes are different lengths. Gem materials with monoclinic crystal systems include jadeite, nephrite, malachite and azurite.

 

Monoclinic System 

 

Triclinic System
The triclinic system has three axes that are different lengths; none of the axes is at right angles. Gems in the triclinic system include turquoise and plagioclase feldspar (labradorite).

Triclinic System 

Cryptocrystalline
Some minerals form in clusters of microscopic crystals; these gemstones are called "cryptocrystalline". Cryptocrystalline materials will usually be translucent to opaque rather than transparent. Chalcedony  is a cryptocrystalline form of  quartz; varieties of chalcedony include agates, chrysoprase and bloodstone 

 

Amorphous
Some gem materials are not crystalline but amorphous in structure; opal and obsidian are common examples. Amorphous materials have no definite internal structure.

 

Organic Gem Materials
Organic gem materials are derived from living forms or are by-products of living things. Coral  is formed from the skeletal material of a small animal that forms hard structures that branch like a plant.Amber  is a fossil resin of ancient pine trees that lived about 30 million years ago. Ivory is taken from the tusks of elephants or walruses.Pearls  form around irritants that invade various mollusks.

CRYSTAL SYSTEMS

Cubic
Three crystal axes of equal length intersect at right angles to each other. e.g. diamond, spinel, garnets.

 

Tetragonal

Three axes intersect at right angles to each other. The vertical axis is of unequal length while the two horizontal axes are of equal length. e.g. zircon, rutile.

 

Hexagonal
Four crystal axes. Three are of equal length and intersect at 60o to form a horizontal plane which the fourth intersects at right angles. The vertical fourth is of unequal length and forms an axis of 6-fold symmetry. e.g. Beryl, apatite.

 

Trigonal
Four crystal axes. Three of equal length intersecting to form a horizontal plane which is intersected at right angles by the fourth axis. The vertical fourth is of unequal length and forms an axis of 3-fold symmetry. e.g. quartz, corundum, tourmaline, dioptase, haematite.

 

Orthorhombic (Rhombic)
Three crystal axes of unequal length interest each other at right angles. e.g. topaz, peridot, Chysoberyl, iolite, sinhalite, andalusite.

 

Monoclinic
Three axes. Two of unequal length intersect each other obliquely to form a plane which is intersected by the vertical third (of unequal length) at right angles. e.g. jadeite, nephrite, diopside, orthoclase feldspar, serpentine, sphene, malachite, spodumene.

 

Triclinic
Three axes of unequal length intersect each other at oblique angles. e.g. turquoise, labradorite.

angles of crystal system

    CRYSTAL SYSTEM SYMMETRY

Singly Refractive: Amorphous -- no crystal structure 

 

			Optic Axis
Cubic	9 planes	4 3-fold	-
	13 axes	3 4-fold	-
	a centre	6 2-fold	-

Doubly Refractive:

			Optic Axis
Tetragonal	5 planes	1 4-fold	uniaxial
	5 axes	4 2-fold
	a centre

 

			Optic Axis
Hexagonal	7 planes	6 2-fold	uniaxial
	7 axes	1 6-fold
	a centre

 

			Optic Axis
Trigonal	3 planes	3 2-fold	uniaxial
	4 axes	1 3-fold
	a centre

 

			Optic Axis
Orthorhombic	3 planes	3 2-fold	biaxial
	a centre

 

			Optic Axis
Monoclinic	1 axis		biaxial
	a centre

 

			Optic Axis
Triclinic	no planes		biaxial
	no axes
	a centre

 

Uniaxial
The optic axis of the crystal is parallel to the main crystal axis. One direction of single refraction.

 

Biaxial

There are two directions of single refraction. (optic axes)

 

GEMSTONES BY CRYSTAL SYSTEM (major ones)

*Diamond simulants, man-made                                        (U) = uniaxial, (B) = biaxial

 

Cubic	Tetragonal(U)	Hexagonal	Trigonal (U)
Diamond Sodalite Fluorite Spinel GGG * Strontium Titanate* Garnet Yttrium Aluminate* Lazurite (Lapis Lazuli) Yttrium oxide* Pyrites Cubic Zirconia*	Apophyllite Idocrase Rutile Scapolite Wardite Zircon	Apatite Aquamarine Beryl Goshenite Morganite	Calcite (marble) Quartz Corundum Rhodochrosite Dioptase Tourmaline Hematite
Orthorhombic (B)	Monoclinic (B)	Triclinic (B)	Amorphous
Andalusite Marcasite Chrysoberyl Peridot Danburite Sinhalite Enstatite Staurolite Iolite Topaz Kornerupine Zoisite	Azurite Nephrite Diopside Orthoclase Feldspar Epidote Serpentine Euclase Sphene Jadeite Spodumene Malachite	Axinite Kyanite Microcline Feldspar Plagioclase Feldspar Rhodonite Turquoise	Amber Chrysocolla Glass Ivory Jet Moldavite Obscidian Opal