What is Gahnite?

 

Gahnite (member of spinel subgroup)

Gahnite is a mineral that is composed of zinc aluminate (ZnAl2O4). It was first discovered in 1807 by Swedish mineralogist Johan Gadolin.

Chemical Formula

The chemical formula for gahnite is ZnAl2O4.

Discovery

Gahnite was first discovered in 1807 by Swedish mineralogist Johan Gadolin. It was named after Swedish chemist and mineralogist Johan Gadolin.

Physical Properties

• Color: green, brown, black
• Crystal System: cubic
• Hardness: 7.5
• Specific Gravity: 4.4

Optical Properties

• Refractive Index: 1.78
• Birefringence: none
• Pleochroism: none
• Dispersion: none

Occurrence by Country

Gahnite is found in a variety of countries around the world, including:

• Australia
• Brazil
• China
• India
• Italy
• Russia
• Sweden
• United States

Healing Properties

Gahnite is believed to have healing properties that can help with:

• Emotional balance
• Stress relief
• Pain relief

Uses

Gahnite is used in a variety of applications, including:

• Ceramics
• Electronics
• Glassmaking
• Jewelry
• Refining zinc

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Epidote Group Information's

 

Epidote Group

The epidote group is a group of related minerals with similar structures and physical and chemical properties. The minerals in the epidote group include:

• Epidote
• Allanite
• Piemontite
• Zoisite
• Clinozoisite
• Tawmawite

Chemical Formula

The general chemical formula for the epidote group is A2B3(SiO4)3(OH).

Discovery

The epidote group minerals have been known since ancient times, but were first recognized as a group in the 19th century. The name "epidote" comes from the Greek word "epidosis", which means "growing together", referring to the common occurrence of these minerals in close association with each other.

Physical Properties

The epidote group minerals are typically green, brown, or black in color and have a vitreous to resinous luster. They have a hardness of 6-7 on the Mohs scale and a specific gravity of 3.2-3.5. They are brittle and have conchoidal fractures.

Optical Properties

The epidote group minerals are typically biaxial positive, with refractive indices of nα = 1.670-1.740, nβ = 1.680-1.750, and nγ = 1.700-1.780. They have moderate to high birefringence and a weak to moderate pleochroism.

Ranking of Rarity

The epidote group minerals are relatively common, with epidote and zoisite being the most abundant members.

Occurrence (countries)

The epidote group minerals are found in a wide variety of geological settings, including igneous, metamorphic, and sedimentary rocks. They are found in many countries around the world, including:

• Epidote: Austria, Canada, France, Italy, Norway, Sweden, Switzerland, USA
• Allanite: Australia, Canada, China, Greenland, Japan, Norway, Russia, USA
• Piemontite: Italy, Switzerland, USA
• Zoisite: Austria, Canada, Italy, Norway, Switzerland, Tanzania, USA
• Clinozoisite: Austria, Canada, Italy, Norway, Switzerland, Tanzania, USA
• Tawmawite: Myanmar

Healing Properties

The epidote group minerals are believed to have a number of healing properties, including:

• Stimulating the immune system
• Enhancing energy and vitality
• Relieving stress and anxiety
• Improving digestion
• Reducing inflammation
• Stimulating creativity and self-expression

Uses

The epidote group minerals have a variety of uses, including:

• As gemstones (e.g. epidote, piemontite, zoisite)
• As collectors' specimens
• In ceramics and glassmaking
• In jewelry-making
• In metallurgy
• In the production of cement and concrete

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Quartz with Anhydrite and clayey soil inclusions

A few days ago, a man brought a brownish-red crystal from Shakaradara, a village in the Kohat district of Khyber Pakhtunkhwa, Pakistan, for testing purposes.

from Shakaradara, a village in the Kohat district of Khyber Pakhtunkhwa, Pakistan

Upon examination, it was observed that the crystal had a pyramid formation and a short hexagonal prism. Additionally, the refractive index of the naturally polished surface was measured to be between 1.542 and 1.550. These characteristics confirmed that the crystal in question was indeed quartz.

from Shakaradara, a village in the Kohat district of Khyber Pakhtunkhwa, Pakistan

To further confirmation, the crystal was subjected to analysis using the Private Raman Spectroscopy facility. The results revealed the presence of Anhydrite mineral inclusions within the quartz crystal. Moreover, the obtained Raman spectra perfectly matched those found in the RRUFF Raman spectra library.

The question regarding the reddish color of this quartz arises from the fact that it is found in an area with clayey soil that has a reddish hue, possibly due to a higher concentration of iron oxide. As the quartz forms, it becomes trapped within this soil, resulting in its distinctive coloration.

from Shakaradara, a village in the Kohat district of Khyber Pakhtunkhwa, Pakistan

Below, you will find the combined (Quartz + anhydrite) and individual anhydrite Raman spectra.

Quartz and Anhydrite combine Raman spectra

Anhydrite Raman Spectra 

Hamid Usman

Gemologist

CIGTL-Gemological Laboratory of Pakistan at Peshawar. 

“Correct me if I’ve misunderstood“

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Worldwide Countries' State Gemstones

Country	State	Gemstone
United States	California	Benitoite
United States	Colorado	Aquamarine
United States	Montana	Sapphire
Australia	Queensland	Opal
Australia	South Australia	Opal
Brazil	Minas Gerais	Topaz
Brazil	Bahia	Ametrine

USA States Gemstones

State	Gemstone
Alabama	Star Blue Quartz
Alaska	Jade
Arizona	Turquoise
Arkansas	Diamond
California	Benitoite
Colorado	Aquamarine
Connecticut	Garnet
Delaware	Sillimanite
Florida	Moonstone
Georgia	Aquamarine
Hawaii	Black Coral
Idaho	Garnet
Illinois	Fluorite
Indiana	Agate
Iowa	Geode
Kansas	Jade
Kentucky	Freshwater Pearl
Louisiana	Opal
Maine	Tourmaline
Maryland	Patuxent River Stone
Massachusetts	Rhodonite
Michigan	Chlorastrolite (Greenstone)
Minnesota	Alexandrite
Mississippi	Flint
Missouri	Galena
Montana	Sapphire
Nebraska	Blue Agate
Nevada	Turquoise
New Hampshire	Smoky Quartz
New Jersey	Zeolite
New Mexico	Turquoise
New York	Garnet
North Carolina	Emerald
North Dakota	Chalcedony
Ohio	Flint
Oklahoma	Barite Rose
Oregon	Oregon Sunstone
Pennsylvania	Azurite
Rhode Island	Bowenite
South Carolina	Amethyst
South Dakota	Rose Quartz
Tennessee	Pearl
Texas	Topaz
Utah	Topaz
Vermont	Grossular Garnet
Virginia	Amazonite
Washington	Petrified Wood
West Virginia	Chalcedony
Wisconsin	Red Granite
Wyoming	Jade

Garnet group , Types of Garnet and its identification Techniques.

Garnet

Garnet is a mineral that comes in many different colors, but is most commonly found in shades of red. Its name comes from the Latin word "granatum," which means "seed," because the small red crystals that garnet often resembles the seeds of a pomegranate.

Garnet has been used for thousands of years as a gemstone and has been highly valued by many cultures throughout history. It was believed to have many healing properties and was used to treat a variety of ailments.

In addition to its physical healing properties, garnet was also believed to have emotional and spiritual healing properties. It was said to help with emotional healing, to promote positive feelings such as love and compassion, and to help release negative emotions such as anger and jealousy.

The garnet group comprises six species, which tall into two series known as the PYRALSPITE series and the UGRANDITE series. 

Chemistry: The six species have the general formula L3M2(SiO4)3. In the PYRALSPTTE series, L may be Mg, Fe or Mn; M is always Al. In the UGRANDITE series, L is always calcium; M may be Cr, Al or Fe. Crystal system and habit: Cubic: Often very perfect crystals. The rhombic dodecahedron and trapezohedron are highly characteristic. When water-worn in gem gravels, the crystals may be almost spherical.

spessartite garnet with quartz 

Garnet

Varieties:

Pyralspite Group:

Pyrope (Cape-Ruby) : Transparent to sub-translucent. Red, orangy-red, purplish-red. 

Rhodolite: (Mid-member between pyrope and almandine) purplish-red or pink to violet. 

Almandine (Carbuncle) : Transparent to sub-translucent. Brownish-red to purplish-red.

Phenomena: Some almandine may display a weak 4 or 6-rayed star. 

Spessartine: Yellowish-orange, red, brownish-red.

 

Malaya: (Mixture of pyrope and spessartine) Tp, pinkish-orange through yellowish-orange. 

Phenomena: A colour-changing garnet (colour variable) consists of a mixture of pyrope and spessartine).

Ugrandite Group:

 Uvarovite: Idiochromatic, colour due to chromium. Attractive 'emerald' green, but crystals suitable for fashioning is extremely rare making it almost unknown as a gemstone.

 

Grossular: Transparent to translucent

 Hessonite: (Cinnamon-Stone, Hyacinth, Jacintti) Brownish-yellow to brownish-red, yellowish-orange.

Origin: Le Chang, Guang Dong Province, China

Sample size: 5 x 5 x 2.7 cm

Origin: Le Chang, Guang Dong Province, China

Sample size: 5 x 5 x 2.7 cm

Origin: Le Chang, Guang Dong Province, China

Sample size: 5 x 5 x 2.7 cm

Tsavorite: Bright bluish-green to yellowing green. Yellow and colourless are also known. (R.I.'s slightly lower.)

Tsavorite

Origin: Merelani Hills, Arusha, Tanzania

Sample size: 1.2 x 1 x 0.7 cm

Tsavorite

Origin: Merelani Hills, Arusha, Tanzania

Sample size: 1.2 x 1 x 0.7 cm

Tsavorite

Origin: Merelani Hills, Arusha, Tanzania

Sample size: 1.2 x 1 x 0.7 cm

Tsavorite

Origin: Merelani Hills, Arusha, Tanzania

Sample size: 1.2 x 1 x 0.7 cm

Hgdrogrossular Translucent to sub-translucent, green, pink, greyish-white ornamental.

Andradite: Transparent to sub-translucent. - Demantoid: Green; rarely yellow (Topaziolite'). - Melanite: Black, nearly opaque.

Demantoid Garnet from Ghazni, Afghanistan.

Demantoid Garnet from Ghazni, Afghanistan.

Phenomena: Rare yellow demantoid may show chatoyancy. Some very dark semi­translucent  to opaque andradite Crystals show iridescence

Demantoid Garnet from Ghazni, Afghanistan.

Physical properties:

Table 15.2 Physical properties of the garnet group.

	Pyrope	Almandine	Spessartine	Grossular	Andradite
Cleavage	none	none	none	none	none
Hardness	7.00-7.50	7.00-7.50	7.00-7.50	7.00-7.50	6.50-7.00
Specific Gravity	3.70-3.90	3.90-4.30	4.12-4.20	3.57-3.73	3.81-3.87
Refractive Index	1.72- 1.76	1.77- 1.82	1.79- 1.814	1.73- 1.76	1.855 - 1.895
Optical Nature	S/ R	S/R	S/R	S/R	S/R
Dispersion	0.002	0.24	0.27	0.028	0.057
Lustre	bright vitreous	bright vitreous	bright vitreous	bright vitreous	sub­ adamantine

 

Other points:

Durability: Good

    Birthstone: January

Pyralspite Series:

 

 

Stones are SR but ADR is common, particularly among the reds.

 PYROPE: Red, orangy-red, purplish-red.

 Inclusions: Low relief and acicular crystals.

Spectrum: Chrome present in best colours; most show presence of some almandine.

Occurrence: South Africa, Sri Lanka, USA, Australia, Russia.

RHODOLITE: (Light. to dark reddish-purple to purplish-red). Mid-member between pyrope and almandine. No internationally accepted name has been found for this section of the series (R.I. l.74-1.77/S.G. 3.74-3.9(Usually shows almandine spectrum). 

Occurrence: Sri Lanka, Tanzania, Zimbabwe. Madagascar, USA.

ALMANDINE: Idiochromatic, colour is due to iron. Some almandine displays a weak 4- or 6-rayed star. The name 'carbuncle' (small coal) is still sometimes applied to almandine cut in the form of hollow cabochons (to lighten colour look).

Inclusions: Needles intersecting (at 110" and 70°) in two (occasionally 3) directions, which may give rise to a 4 or 6-rayed star: both well-formed and rounded crystals; zircon halos.

    Spectrum: Colour is due to iron. Typical spectrum has bands at 505,        527 and 575 nm. A series of weaker bands may be seen on either side.

                             Almandine Garnet Spectrum

                             Almandine+ Spessartine Garnet

Occurrence: India, Sri Lanka, Brazil, Madagascar, Tanzania, Zambia, Pakistan. USA.

MALAYA (Mali): is a bright orange garnet and a member of the pyralspite series (R.I. 1.75 to 1.76) and a rare colour-changing garnet (bluish-green in daylight/purplish-red in incandescent) with an R.I. of 1.765, S.G. 3.88, consists primarily of a mixture of pyrope ­spessartine garnet.

Occurrence: East Africa.

SPESSARTINE: Colored by manganese. Yellowish-orange, red, brownish-red.

Inclusions: Wavy liquid droplets, and 2-phase inclusions. 

       SPESSARTINE Garnet Spectrum

Occurrence: Sri Lanka, Africa, Namibia, Brazil, Burma, Madagascar, India, Australia, USA

Ugrandite Series:

 GROSSULAR: Transparent to translucent.

HESSONITE: Inclusions: Classic granular appearance caused by a profusion of rounded crystals (may he. apatite or zircon) and oily/treacly internal effect.

Occurrence: Gem gravels of Sri Lanka, Brazil, Canada, Kenya (relatively clean).

TSAVORITE: Color is attributed to the presence of vanadium but many stones appear red under 'the Chelsea Color Filter due to a trace of chrome. Colourless and yellow grossular R.Is are slightly lower at 1.750 to 1.762

Occurrence: Kenya (Tsavo ), Tanzania, Pakistan.

HYDROGROSSULAR: Translucent to opaque green and pink massive material. Chromium is the cause of colour in some green varieties (may appear pinkish through the Chelsea Colour Filter). 

Inclusions: May show black inclusions in translucent pink or green background.

Occurrence:, New Zealand, USA, Pakistan

 ANDRADITE: 

DEMANTOID: Green, yellowish-green, may appear reddish under the CCF. Yellow demantoid very rare. Stones are usually less than 1 carat. Inclusions: Classic 'horsetail' (fibrous byssolite). 

Occurrence: Green -  (Urals - found as rolled pebbles, fine green material now rare), Italy, Zaire. Yellow - Italy, Switzerland. Pakistan

 

Horsetail Inclusions in Demantoid garnet  Origin: Khuzdar district, Baluchistan Province, Pakistan.

Horsetail Inclusions in Demantoid garnet  Origin: Khuzdar district, Baluchistan Province, Pakistan.

Horsetail Inclusions in Demantoid garnet  Origin: Khuzdar district, Baluchistan Province, Pakistan.

Horsetail Inclusions in Demantoid garnet  Origin: Khuzdar district, Baluchistan Province, Pakistan.

Horsetail Inclusions in Demantoid garnet  Origin: Khuzdar district, Baluchistan Province, Pakistan.

Horsetail Inclusions in Demantoid garnet  Origin: Khuzdar district, Baluchistan Province, Pakistan.

Horsetail Inclusions in Demantoid garnet  Origin: Khuzdar district, Baluchistan Province, Pakistan.

Horsetail Inclusions in Demantoid garnet  Origin: Khuzdar district, Baluchistan Province, Pakistan.

KEY POINTS

 

1.    Almandine from Pyrope                                  RI, Spectra

2.    Almandine from Rhodolite                               RI, Colour

3.    Almandine from Malaya                                   RI, Spectra, Color change

4.    Almandine from Spessartine                           Colour, spectrum

5.    Almandine from Hessonite                              Colour, RI, Spectrum

6.    Rhodolite from Pyrope                                     Colour, RI, Spectrum

7.    Rhodolite from Malaya                                     Colour, Spectrum, RI

8.    Pyrope from red spinal, syn. Spinal                 Magnification, RI, F

9.    Pyrope from Hessonite                                    colour, spectra ,RI,F

10. Malaya from Hessonite                                     Colour, spectra, RI

11. Demantoid(green) from Tsavorite (green)        RI, Spectrum, Magnetic

12. Spessartine(orange) from Hessonite               RI, Spectra

Note: If the garnet RI is 1.740 to 1.770, and purple to purples to red or     pink colour and an almandine spectrum, it should be identified as       rhodolite garnet