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Grandidierite: Rare Gemstone From Madagascar – Origins, Properties, and Market Trends
Introduction to Grandidierite Gemstone
Grandidierite is one of the rarest gemstones with blue blue-green hue. It is popular for its remarkable pleochroism and rarity. Prior to recent discoveries, significant sizes of facet-grade quality stones were almost nearly non-existent. Grandidierite was first discovered in 1902 by a famous mineralogist ” Antoine François Alfred Lacroix”. After discovery, the gemstone was given a name in honour of Alfred Grandidier. He was a renowned explorer of Madagascar. The very first sample of grandidierite was found in the island’s southern coastal region near Tolagnaro (formerly Fort Dauphin).
The Discovery and Geology Grandidierite
As we have indicated above grandidierite was first discovered by French mineralogist Alfred Lacroix in 1902 in Madagascar.
Recent Discoveries: Recent discoveries of the gemstone deposits were found in 2016 near Tranomaro, Madagascar. This also has significant availability of facet-grade stone coming in a crystallised form. Even from this location, a small size of rough material would be suitable for faceting. Out of 800 kilo gram of rough stone, only 50 to 60 were of crystal form and only 1 to 2 percent of these crystalized gems are considered for top quality. The IGS source also notes, “Recent discoveries of transparent material may bring more to the market.
Geology:
|
Geological Aspect |
Details |
|---|---|
|
Occurring and Formation: |
Aluminous boron-rich rocks, pegmatites, gneisses |
|
Conditions: |
High-temperature, low-pressure metamorphism |
|
Primary Source |
Tolagnaro (Fort Dauphin), Madagascar |
|
Secondary Sources |
Sri Lanka, Malawi, Namibia, Algeria |
- This blue-green rare gemstone is mainly formed in aluminous boron-rich pegmatites under high pressure often alongside minerals like sapphire and tourmalines.
- It is formed in metamorphic rocks.
- Crystals can be up to 8 cm in length.
- In massive occurrences, the crystals of grandidierite are elongated and not well formed.
- Mineral deports are normally described as irregular. They are distributed in many discontinuous veins. Normally they are found very sporadically.
- Deports are found close to the surface, around about 15 meters down.
- Deposits are normally extremely limited.
Understanding the Physical and Chemical Properties of Grandidierite
Grandidierite physical properties are here :
- Chemical Composition: (Mg,Fe)Al3(BO3)(SiO4)O2
- Color: Bluish-green to greenish-blue. iron content giving it bluish-green to greenish-blue hues. The most valuable colour would be a vivid turquoise tone.
- Hardness: 7 to 7.5
- Cleavage: Perfect in one direction, good in another
- Transparency: Often translucent to opaque, with transparent is the most rare
- Luster: Vitreous to sub-vitreous.
- Pleochroism: Strong: dark blue-green, colourless, dark green
- Specific Gravity: 2.85-3.00
- Refractive Index: 1.578-1.639 , 1.583-1.639 (with IGS), 1.590-1.639 (with GIA).
These Grandidierite properties make it a scientifically intriguing specimen.
Grandidierite Origins: Global Mining Sources and Localities
- Madagascar: The most significant sources are found near Tolagnaro in the southern region. Tranomaro also close to Cap Andrahomana in Madagascar (located 60km away from Cap Andrahomana) area has also new deposits which are also producing more facet-grade transparent crystals. This location produces 95% of Grandidierite. The Smithsonian Institution describes the region as a “geological wonder,”.
- Sri Lanka: Some Grandidierite have also been recovered from alluvial deposits.
- Namibia and Myanmar: Minor deposits of the stones have been found in Namibia and Myanmar but they are extremely low grade deposits. .
- Other localities are Sri Lanka, New Zealand, in some other parts of Africa, United States (New York, Wyoming), Algeria, Antarctica, Italy, Malawi, Norway and Slovakia. However these locations have lower grade and not crystallized material. According to Mindat.org data, Madagascar is the prime source of facet grade or gem-quality Grandidierite.
Is Grandidierite a Good Investment? How valuable is Grandidierite?
The stone is getting attraction in the global gemstone market. There is increasing demand for this rare gemstone due to its unique turquoise color and aesthetic appeal.
- Grandidierite Price: Prices of any stone depends on color, clarity, size and color. According to National Jeweler, top-grade grandidierite fetch 20,000–50,000 USD per carat. Even translucent quality of the stone is highly valued. Grandidierite’s value is increased with size and clarity. The largest known stone is 763.5-carat faceted grandidierite as known by GIA which is extremely rare. Reports from the Gemological Institute of America (GIA) are mentioning Grandidierite’s ranking among the top ten rarest gemstones globally.
- Collector Value: With its rarity among other colored gemstones, Grandidierite is highly demanded by collectors and gemstone investors. However, collectors prefer quality over quantity. Grandidierite is one of the ” top 10 rarest gemstones as per GIA along side painite and taaffeite.
- Auction Records: A 7.87-cat Grandidierite was sold for $138,000 at a 2015 Sotheby’s auction. Another 6.95-carat grandidierite setting with diamond ring was sold at Bonhams in 2021 for US$75,312.50 (Bonhams).
- Limited Supply: Limited mining activity along with small yields indicates that Grandidierite remains a rare commodity.
Identifying Synthetic Grandidierite and Common Imitations
Gemological Institutions like the GIA and others are actively studying Grandidierite characteristics and its new finds to better understand its properties and confirm its identification.
- Synthetics: Till now, there is no known syntehtic stone in the market or set in jewelry. There is no commercially known syntehtic stone exists. This may be because of its complex composition. Though scientists have synthesized grandidierites for their research related to ominelite and werdingite.
- Imitations: Some stones may look-alikes such as apatite, tourmaline, or even treated glass may be misrepresented as Grandidierite.
- Treatments: There are also no known treatments or enhancements for grandidierite gemstones. The stones found in the market are normally 100% natural and original.
- Similar Stones: There are other stones such as lzulite which may look like grandidierite which show similar pleochroism (colorless/blue/dark blue). However, lazulites have somewhat higher RI (Refractive Index) and specific gravity (SG). Whereas Grandidierites have greater hardness which allows gemologists to separate between the two
- Testing: Gemological tools like spectrometers and refractometers is essential to use them for identification of the stones. Laboratories such as GRS (GemResearch Swisslab) and the GIA offer reliable certification.
How can Grandidierite be identified?
Indentifying a grandidierite involves combination of gemological properties. The strong trichroic pleochroism is a key indicator which shows dark blue-green, colorless and dark green depending on its angle. The gems identification factors are RI (1.583 – 1.639), SG (2.85-3.0) and hardness 7.5 on Moh Scale.
How to Buy Grandidierite Gemstone?
While buying Grandidierite stone, follow the following:-
- Certification: Get popular lab certifications from respected institution (GIA, GRS, etc.)
- Transparency and Color: Go for stones with vivid blue-green hues and minimal inclusions.
- Origin Disclosure: Look for verification of origin of the stone, preferably from responsible mines in Madagascar.
- Dealer Reputation: Look for dealer reputation in the market before buying. Look for customer reviews online if buying online.
FAQ and Quick Facts About Grandidierite
Q: Why is crystallized and faceted Grandidierite so rare and valuable?
A: The deposits of gem grade stones are limited. High demand contribute to its rarity.
Q: Can Grandidierite be Used for everyday jewelry?
A: Its 7.5 Mohs hardness makes it durable for jewelry wears. This hardness of the stone is makes it very resistant to scratching and is described as ideal for jewelry use.
Q: Where is Grandidierite found?
A: The stone is mainly found in Madagascar, with very very minor and limited occurrences in Sri Lanka, Myanmar, Namibia and other areas.
Is Grandidierite a good investment?
A. Its rarity and collector demand which makes it investment grade stone.
Q: Where can I buy genuine Grandidierite?
A: There are lot of gemstone dealers avaialble selling the stone. One of them popular is Folkmarketgems.com who are popular and trusted gemstone dealers. They focus on ethical gemstone hunting both in raw and colored loose gemstones.
Conclusion
Grandidierite is one of the rare and beautiful colored gemstones. From its prime locations in Madagascar, its status remains one of the demanded rare gemstone, this blue-green gemstone continues to fascinate collectors and investors alike. Buyers must look for certified stone and ethically sourced gem. With careful buying, gradidierite can be one of the stunning addition to any mineral collector with a promising gem investment.
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