India – Alexandrite, Diamond (Panna), and Garnet
Indian gem deposits – Andhra Pradesh alexandrite and chrysoberyl, Panna kimberlite diamond, Orissa garnet; geological context; Koh-i-Noor attribution qualified.
Introduction
India's gem production reflects its ancient and diverse Precambrian geology.
Andhra Pradesh (Visakhapatnam and East Godavari districts) hosts chrysoberyl and
alexandrite in acidic pegmatites intruding Eastern Ghats khondalites; chromium from
the metamorphic country rock produces the Cr³⁺ colour-change effect. Madhya Pradesh's
Panna Diamond Belt contains the country's only significant primary diamond source:
the Majhgawan and Hinota kimberlite pipes (~1100 Ma), which supply both in-situ and
alluvial diamond recovered by NMDC. Famous historical diamonds including the Koh-i-Noor
are traditionally attributed to the Golconda-Panna alluvial region, though this
attribution is historical tradition rather than confirmed by modern gemmological
peer-reviewed analysis. Orissa (Odisha) and Tamil Nadu yield almandine-pyrope garnet
from Proterozoic metamorphic basement; Tamil Nadu also produces star garnet with
4- and 6-rayed asterism from rutile inclusions.
Kashmir sapphire, India's most celebrated gem locality, is covered in a dedicated
file. [1][2]
Geological Settings
| Region | Province | Geological Setting | Gems |
|---|---|---|---|
| Visakhapatnam / East Godavari | Andhra Pradesh | Acidic pegmatites in Eastern Ghats khondalites | Chrysoberyl, alexandrite |
| Panna District | Madhya Pradesh | Majhgawan and Hinota kimberlite pipes (~1100 Ma) | Diamond |
| Orissa (Odisha) | Various districts | Archaean basement; Precambrian metamorphic rocks | Pyrope and almandine garnet |
| Tamil Nadu | Southern India | Garnet-bearing metamorphic basement | Star garnet (almandine-pyrope) |
Alexandrite – Andhra Pradesh
Eastern Ghats chrysoberyl and alexandrite:
Geological Context
- Chrysoberyl (BeAl₂O₄) occurs in acidic pegmatites intruding khondalites
(metamorphic granulites) of the Eastern Ghats mobile belt - Kasipathi (1996) confirmed: "Chrysoberyl occurs in the acidic pegmatite
intrusive into the khondalite of the Eastern Ghats of north coastal Andhra Pradesh" [1] - The pegmatite supplies Be and Al; the ultramafic country rock or metamorphic
khondalite supplies Cr for alexandrite variety formation
Properties
- Colour change: Green in daylight / red in incandescent (Cr³⁺ in BeAl₂O₄)
- Fluorescence: Red LWUV (Cr³⁺)
- RI: 1.745–1.757 (α), biaxial positive
- SG: ~3.73; Hardness: 8.5
Origin Determination Note
- Indian alexandrite is noted in the trade for its colour-change effect
but fine colour change quality – the definitive balance of green-to-red
response – is generally considered less striking than fine Ural (Russian)
material - This is a generalisation based on trade consensus: the sourcing literature
does not provide a peer-reviewed comparison of Indian vs Ural quality as
a verified gemmological fact; individual stones vary
Diamond – Panna District
India's only significant primary diamond source:
Geology
- Panna Diamond Belt, Madhya Pradesh: kimberlite pipes (Majhgawan and Hinota,
~1100 Ma) emplaced in the Baghain Sandstone of the Vindhyan Supergroup [2] - The basement Bundelkhand granitoids underlie the Vindhyan sedimentary cover;
diamonds occur both in the primary kimberlite and in secondary alluvial
and conglomerate deposits derived from kimberlite erosion - Active mining by NMDC (National Mineral Development Corporation)
Koh-i-Noor Attribution – Critical Note
- Various famous diamonds including the Koh-i-Noor, Regent (Pitt Diamond),
and others are traditionally attributed to the alluvial workings of the
Golconda-Panna region of central India - This attribution is TRADITIONALLY ACKNOWLEDGED in historical and gem trade
literature; it is NOT confirmed by modern gemmological peer-reviewed analysis - The Rau (2007) paper on the Panna Diamond Belt confirms the geological
framework but does not attribute any specific famous diamond to Panna [2] - For examination purposes: state that famous historic diamonds including
the Koh-i-Noor are "traditionally attributed to" the Golconda/Panna
alluvial region of India – not that their Indian origin is a confirmed fact
Koh-i-Noor Qualification
Diamond Origin Determination Caveat
Orissa Garnet
Garnet from Orissa (Odisha):
- Pyrope and almandine garnet from Proterozoic metamorphic and Archaean basement
of Odisha; artisanal production - Tamil Nadu produces 4-rayed and 6-rayed star garnet (almandine-pyrope with
rutile asterism inclusions); India is a significant source of star garnet [3] - No diagnostic origin-determination criteria specific to Indian garnet at the
bench level; provenance documentation required
References
- ↑ 1. Kasipathi, P. (1996). Chrysoberyl from Visakhapatnam and East Godavari Districts, Andhra Pradesh. Journal of the Geological Society of India, 48(4). DOI: 10.17491/jgsi/1996/480412.
- ↑ 2. Rau, H. (2007). Panna Diamond Belt, Madhya Pradesh — A Critical Review. Journal of the Geological Society of India, 69(3). DOI: 10.17491/jgsi/2007/690306.
- ↑ 3. Shigley, J. (2010). Gem Localities of the 2000s. Gems & Gemology, 46(3), 188–216. DOI: 10.5741/gems.46.3.188.