Standard Gemological Instruments and their use

 

Gemological Instruments and their use

S#	Name of Instrument	Use
1	Polariscope	Polariscope is useful instrument to determine whether the stone is singly refractive (SR) or Double refractive (DR)
2	Refractometer(portable)	Refractometer is use for Refractive index (RI) of gemstone.
3	Dichroscope (portable)	Dichroscope is use for Pleochroism in gemstones. If the gemstone is pleochroic then it should be Double refractive.
4	Spectroscope(portable)	Spectroscope is use for to determine the spectrum of gemstones. With the help of spectroscope we can easily separate same colors gemstones for example ruby, red glass and garnet.
5	Ultraviolet Lamp (portable)	Ultraviolet is use for to determine Fluorescence effect in gemstones. With the help of this instrument we can separate natural blue sapphire from synthetic blue sapphire.
6	Chelsea filter (portable)	Chelsea filter is use for separating emerald from its imitations and detecting chromium in green stones and cobalt in blue stones.
7	Microscope  / Hand lens(portable)	Use for study of inclusions in gemstones. It is one of the most powerful tool in ordinary gemology tools.

 

How gemstone weight? which unit of weight is used?

Weight and price

UNIT OF WEIGHT

Ø    Gemstones are sold by weight.

Ø    Large ornamental and rough material may be sold in kilogram (Kg) or gram (gm).

Ø    Gemstone weight is given in Carats.

Ø    Carat is denoted by “Ct”       

                               1 Ct = 0.2 gm

                               5 Ct = 1.0 gm

Ø    Each carat is split into 100 cents or  points 

1.00 Ct = 100 cents or points

0.50 Ct = 50 cents or points

0.01 Ct = 1 cents or points 

Basic Terms used in Gemology

 

Basic Terms used in Gemology

Real or Natural gemstones: Real or Natural Gems are those which are entirely the product of nature and unaltered by humans in any way, except for ordinary cutting and polishing.

Treated gem: Any gem material which has been altered by humans, beyond ordinary cutting or polishing. For example Diffusion sapphire, Glass filling Ruby, dying, heat treatment etc.

 

Synthetic gems: Same as natural gem ( in terms of composition, structure, properties and appearance), except made by man. Or The Gems which have natural counterpart. For example Synthetic Ruby, sapphire etc.

How to grown synthetic quartz in laboratory by hydrothermal process?

 

Simulant or imitation: A material ( Natural or Synthetic), Which has the same appearance as the gem it imitates(look like) but different chemical composition. For example Cubic Zirconia imitating Diamond, Red Garnet is the imitation of Ruby.

 

Assembled gems or composite gems: A gem material (Natural or Synthetic), which is produced by assembling two or more pieces of the like or unlike material along a distinct junction. For example opal triplet, garnet/glass doublet.

What is gemstone? define beauty , rarity and durability in gemstone.

What is Gemstone?

Gemstone is a natural, inorganic or organic substance that has substantial beauty, rarity, and durability.

Organic Gems: An organic gem is one that was made by living things, present or past. Examples include pearls, coral, jet, ivory, shell and amber.

Inorganic Gems: Inorganic gems are those which are created by geological process and (usually) dug from the ground.

1.Beauty 2. Rarity 3. Durability

1. Beauty

 To be considered a gem, a material must possess to a large degree this preliminary qualification. Beauty in gemstone may depend on such qualities as color, transparency, luster, brilliance, pattern, optical phenomena and, in some cases, distinctive inclusions.

2.      Rarity

This is a valued attribute of gems. It is natural for man to esteem most highly the things, which are hard to obtain, and this can come about if the gemstone is simply unavailable in the marketplace, or genuinely scarce(limited or short supply) in nature, even if it does not possess qualities above others of similar beauty. A good example of this is taaffeite, which is not especially attractive, (Usually a pale reddish-violet color like some spinels), but will fetch (take) a very high price because of its rarity.

3.      Durability

Durability depends upon on three factors

1. Hardness 2. Toughness 3. Stability

1) Hardness is the ability to resist scratching. Commonly measured on the "Mohs" Scale of 1 - 10. Talc lowest (1), diamond highest (10).

Moh's Hardness scale 

Mohs hardness scale

how to grow synthetic Emerald in laboratory?

how to grow synthetic Quartz in laboratory?

2) Toughness is the ability to resist breaking or chipping. This property is measured in relative terms rather than on a numeric scale: sphalerite is fragile, diamond is moderately tough and jade is exceptionally tough. The lower the toughness of a gem the more susceptible it is to damage by the kinds of blows and knocks that are inevitable with frequent wear and use.

3) Stability is resistance to changes caused by environmental factors such as temperature, chemicals and light. Apatite is temperature sensitive, pearls are chemically sensitive, and Kunzite's color is unstable in strong light. Unstable gems exposed to common factors of the natural or man-made environment are likely to break, change color, or lose their luster.

What is mineral?

Mineral is defined as the substances which have the following catachrestic

• Naturally occurring  

• Inorganic

• Defined chemical composition

• Orderly atomic structure.

 

What is Gemology and gemologist and career prospects in gemology?

Gemology is the scientific study of gemstones. It is concerned with the study of gem materials, including identification, testing methods and the basic knowledge of crystallographic, chemical, physical and optical properties of the gemstones.

What is a Gemologist?

A gemologist is someone who can identify the gemstone with the help of Instruments. Gemologists give a business added credibility.

Career prospects in Gemology: Following are the career prospects for a Gemologist:

• Entrepreneurship in Gemstone dealing (the semi precious varieties do not cost a great deal!)
• Working as a gemologist with any of the renowned jewelers.
• Working or setting up your own laboratory for gem testing or gem identification.
• Pursuing further research in gemology or diamond grading.
• Creating your own designs in traditional or modern jewelry.
• Working as jewelry designers in fashion institutes.
• If you are a geologist you can focus your doctorate or post doctorate studies on diamonds or gemstones.
• Start with a lab setup for creating synthetic gems.
• Dealing in organic gems like corals and pearls is a different business avenue in itself.

What is Lapis Lazuli and its real or fake?

 

Lapis Lazuli 

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The ornamental material lapis lazuli can be classed as a rock rather than as a single mineral species. It consists of lazurite, sodalite, nosean and haüyne, the four members of the sodalite mineral group. These species occur mainly in association with leucite or nepheline in nepheline syenites, phonolites and related undersaturated igneous rocks (Deer, Howie and Zussman [DHZ] Rock-Forming Minerals, second edition, vol. 4B (2004; ISBN 1862391440)). Framework silicates. Silica minerals, feldspathoids and the zeolites. Lazurite and sometimes sodalite are occasionally found in contact metamorphosed limestones. The name lapis lazuli is usually given to the typical lazurite-rich rock which usually includes brassy yellow pyrite crys- tals, calcite and a colourless pyroxene. Nassau (2000) describes how it was discovered that the colour of lapis lazuli was derived from three poly- sulphide units of three sulphur atoms having a single negative charge. The S ion in sulphur has a total of 19 electrons in molecular orbitals and a tran- sition among these orbitals produces a strong absorption band in the yellow at 600 nm, giving a blue colour with yellow overtones. The blue colour is increased by increasing the sulphur and calcium contents. A green colour results from insufficient sulphur. The process can be described as an anion–anion charge transfer.

Lapis lazuli has been mined in the Sar-e-Sang district in Badakhshan,

north-east Afghanistan, for many centuries. The lazurite occurs in a rock with diopside, calcite and pyrite. Lapis lazuli is localized in two horizons of magnesian marbles near the centre of the Hindu Kush granitic massif (DHZ, op. cit.). Beds and lenses of lapis lazuli at Sar-e-Sang were described as up to 4 m thick and to extend for 400 m within a skarn formed under relatively high conditions of pressure and temperature

Lapis lazuli in the Baffin Island deposit at Lake Harbour shows a pri- mary coating of deep blue to a paler blue and a teal green, not usually recorded for lapis lazuli. In this deposit Hogarth and Griffin (Lapis lazuli from Baffin Island-a Precambrian meta-evaporite, Lithos 11, 37-060, 1976) and Cade et al., Abstracts of the Eighteenth General Meeting of the International Mineralogical Association, Edinburgh, 2002. The deposit at Lake Harbour is in a dolomitic marble.

Lapis lazuli is found in the North Italian Mountains of Colorado, USA, where the occurrence is in impure marble layers near their contact with Tertiary quartz monzonite and quartz diorite of the Italian Mountain stocks (Hogarth and Griffin, Contact-metamorphic lapis lazuli: the Italian Mountain deposits, Colorado, Canadian Mineralogist 18, 59–70, 1980).

Lapis lazuli is being mined from a limestone-granite contact (elevation 3500 m) in the headwaters of the Cazadero and Vias rivers, Ovalle, Coquimbo, Chile, close to the border with Argentina. The lapis here is paler in colour and associated with wollastonite rather than diopside as in the Baikal deposits, Russia. The Chilean lapis contains phlogopite, sodalite, calcite and pyrite and is described by Borelli et al., Caratterizzazione del lapis- lazuli (Borelli et al., La Gemmologia 11(4), 24–27, 1986 and Coenrads and Canut de Bon, Lapis lazuli from the Coquimbo region, Chile, Gems & Gemology 36, 28–41, 2000.

The properties of lapis lazuli are helpful in identification. The hardness is usually between 5 and 6, the RI near 1.50 and the SG 2.7–2.9; if a signifi- cant amount of pyrite is included the figure will be higher. Under LWUV some specimens may show a streaky orange fluorescence (Chilean speci- mens in particular). Under SW lapis may show a pinkish response. If touched with HCl a characteristic rotten egg smell will result.

Using a ceramic technique Pierre Gilson has manufactured a product known for convenience as synthetic lapis. Specimens may or may not contain added pyrite. The material has been found to be porous with a lower SG than natural lapis, near 2.46. The RI is close to 1.50 but the shadow-edge is vague. The Gilson material is discussed in a paper in the Journal of Gemmology 19(7), 1985: the material should be regarded as an imitation though it has been offered as synthetic. Ultramarine and hydrous zinc phosphates are the main components. An imitation of lapis by Verneuil-grown spinel has higher constants (SG near 3.6, RI near 1.73) – interestingly gold flecks have sometimes been added to simulate pyrite!

Dyed howlite has also been used as an imitation though it is easily detected by an orange fluorescence after the dye has been removed. A dyed jasper with the quartz SG near 2.65 was at one time known as Swiss lapis.

A cobaltian polycrystalline material has a granular structure and shows red through the Chelsea filter. A dyed blue quartzite has also been used as a lapis imitation. In many cases of dyed specimens acetone will be found to remove the dye which has been found to penetrate about 1.5 mm from the surface. One interesting imitation was found to be dyed dolomite with RI between 1.50 and 1.68 and SG 2.85.

The best contemporary account of lapis from the classic deposits of Afghanistan is given by Bowersox and Chamberlin, Gemstones of Afghanistan, 1995 (ISBN 0945005199). The Badakhshan deposits are in the north-east of the country in a mountainous area and occur in mainly plutonic and metamorphic rocks which are cut by deep valleys. The lapis deposits are situated along the valley of the Kokcha river, on the Blue Mountain on which folding and faulting occurred in the Cretaceous period when intrusion by a diorite porphyry took place. The steep valley slopes of the upper Kokcha river in the eastern Hindu Kush are gneisses with thick intercalations of greyish white dolomitic marble. Lenses of light to dark blue lapis frequently occur. In Lapidary Journal 38(11) Emmett explains that the lapis occurs in grey lenses of calcite- dolomite skarn formed by contact metamorphism of impure limestone and high-grade metamorphic sequence of Precambrian rocks resulting from the intrusion of masses of molten granite, causing the formation of marble. The skarn lenses are more than 1–4 m thick and are underlain by gneiss. One of the classic mines is set in strata of black and white limestone. The crystalline series in which the lapis is found consists of gneiss, leptinites and cipolin marble in a heavy layer, amphibolites, pyroxenites and peridotites in which the lapis is found in disseminated veins.

Buyer's Guide to Lapis Lazuli, Spotting Real & Fake Stones

Buying and Polishing Lapis Lazuli From Afghanistan by GIA