Inclusions in Indian Gemstones

An overview of inclusions in Indian Gemstones

Author: Gagan Choudhary

Introduction

India is homeland for many fabulous historic diamonds, especially from the Great Golconda diamond field in central-southeast India, now known as Andhra Pradesh and many exquisite blue sapphires from Kashmir. India is also known to produce some fine qualities of various coloured gemstones, including extraordinary sizes of star rubies from Mysore in the Karnataka state.

Chrysoberyl and alexandrite from Odisha (Orissa) and Andhra Pradesh, pyrope-almandine garnet from Rajasthan and Odisha, Labradorite and fluorite from Jharkhand (formerly in the state of Bihar), iolite from Odisha, moonstone from Tamil Nadu, topaz from Odisha, etc. have gained a lot of popularity in past decades.

Due to the diverse geological setting, India hosts a large number of minerals and gemstones; hence, a wide range of inclusions are also found in these gemstones. This paper overviews the crucial types of inclusions found in various gemstones mined in different locations of India. These gemstones display a wide range of mineral inclusions in various forms; rutile and zircon being the most common ones. Other mineral inclusions found include feldspar, mica (biotite), tourmaline, ilmenite, hematite, magnetite, spinel, chromite, etc. Fluid inclusions such as two, three or multiphase are also a common feature in stones like beryl and topaz. Some of these are simple two phases while some form complex patterns with jagged edges. Structural features such as twinning planes, cleavages, growth zoning and colour zoning are also common features in Indian gemstones.

Table 1: Common types of inclusions seen in Indian gemstones

Table 1: Common types of Inclusions seen in indian gemstones
Inclusion Type	Examples
Solid	Crystals (euhedral to anhedral): zircon, rutile, apatite, calcite, quartz, hematite, enstatite, spinel, tourmaline, magnetite, etc. Flakes / platelets: hematite, hornblende, magnetite, ilmenite, mica, Needles: rutile, tourmaline, riebeckite in sagenitic quartz Exsolved inclusions: rutile in the form of long / short silk / needles in corundum and garnet; boehmite along twin planes of corundum, albite along twin planes of feldspars, lepidocrocite along cleavage planes of scapolite, etc
Fluid	Phase: Complex fluid inclusions - 2/3 phase with jagged edges. 3-phase inclusions with cubic colourless crystal (such as Halite). Much of the phase inclusions contain CO2 liquid and gas. Elongated tube-like phase inclusions are common Liquid films: Commonly present along the pinacoidal faces as in Beryl Fingerprints / Feathers: Common in most of the stones with mono-phase or 2-phase droplets
Structural	Growth / Colour Zoning: Common in most of the stones; more prominent in beryl, chrysoberyl, corundum, kyanite, hessonite garnet, etc Cleavages: Clearly visible, where present Twinning Planes: Clearly visible, where present as in corundum and feldspar
Others	Other inclusions include etch channels/ tubes, fissures, cloudy inclusions, banding, iron stained fractures / films, etc.

Presented here are the visuals of some common inclusions in Indian gemstones:

Solid Inclusions

Euhedral rutile crystals in ruby from Karur, Tamil Nadu (64x)

Flaky rutile crystals in ruby from Raipur , Chhattisgarh (48x)

Rounded colourless zircon crystals in ruby from Karur, Tamil Nadu (64x)

Euhedral colourless apatite crystals in ruby from Odisha(64x)

Transparent mocrystal in ruby from Karur, Tamil Nadu (80x)

Reflecting hematite crystal in ruby from Raipur, Chhattisgarh (80x)

Fine oriented platy magnetite crystals in spectrolite from Bihar/ Jharkhand (64x)

Brown platy crystal (possibly axinite) associated with black magnetite in spectrolite from Bihar/Jharkhand (100x)

Prismatic rutile crystals in fuchsite from Tamil Nadu (48x)

Acicular apatite crystals in almandine garnet from Rajasthan, reminiscing sagenitic quartz (24x)

Acicular apatite crystals in almandine garnet from Rajasthan had pyramidal terminations (80x)

Rounded and anhedral calcite crystals in hessonite from Odisha(64x)

Calcite crystals in hessonite from Odisha appear birefringent under cross-polars (64x)

Quartz crystal in hessonite from Odisha(100x)

Euhedral calcite crystal in spinel from Odisha(100x)

Brown dendritic crystals with squarish profile in serpentine from Odisha(80x)

Sub-rounded zircon crystals with radiation induced stress crack in iolite from Odisha(100x)

Hexagonal platelets of hematite in iolite from Bihar / Jharkhand (100x)

Euhedral rutile crystal in kyanite from Tamil Nadu (100x)

Rounded colourless zircon crystals in kyanite from Tamil Nadu (80x)

An elongated sub-hedral twinned zircon crystal in brown zircon from Odisha(100x)

Euhedral blackish zircon crystal attached with brown enstatite crystal in brown zircon from Odisha(100x)

Golden rutile fibres in sagenitic quartz from Odisha(64x)

Acicular ‘schorl’ tourmaline in sagenitic quartz from Odisha(80x)

Long and short rutile silk/platelets intersecting at 60/120 deg, with re-entrant angle in ruby from Karur, Tamil Nadu (80x)

Long rutile silk / needles intersecting at 70/110 deg in almandine garnet from Rajasthan (64x)

Multiple sets of short needle–like inclusions causing eight-rayed star in orthoclase feldspar from Tamil Nadu (64x)

Fine long and short needles of possibly magnetite or hornblende intersecting at 105/75 deg causing 4-rayed star in diopside from Tamil Nadu (48x)

Dendritic platelets of ilmenite oriented along the basal plane of beryl from Karur, Tamil Nadu (80x)

Orange brown platelets of hematite in sunstone from Karur, Tamil Nadu (48x)

Orange brown hematite platelets in sunstone appear highly iridescent in reflected light (80x)

Iolite from Odisha with fine whitish dendritic platelets oriented in planes (48x)

A multi-phase inclusion oriented along the ‘c’ axis in aquamarine from Andhra Pradesh (80x)

Complex 3-phase inclusions with jagged edges oriented along the ‘c’ axis in aquamarine from Andhra Pradesh (80x)

3-phase inclusion in diopside from Rajasthan contains cubical (salt) crystal and a bubble (100x)

3-phase inclusion in fluorite from Bihar contains cubical (salt) crystal and a bubble (100x)

Elongated multi-phase inclusion in topaz from Odisha (80x)

2-phase inclusions in planes in aquamarine from Karur, Tamil Nadu. Similar inclusion is seen in topaz from Odisha(48x)

Fine iridescent liquid films oriented along the basal plane of beryl from Karur, Tamil Nadu (64x). Photo: M.B. Vyas

Reflecting and iridescent growth tubes along the ‘c’ axis of beryl from Karur, Tamil Nadu (64x). Photo: M.B. Vyas

An emerald crystal from Odisha displaying strong colour zones with a central colourless core (16x)

Complex pattern of growth zoning in Hessonite garnet from Odisha with rhomb-shaped (dodecahedral) patterns from various centres (48x)

Hexagonal zones of rutile dust are a common feature in corundum from India (16x)

Planes of fine discs / pinpoints along pyramidal faces in this brown zircon from Odisha (40x)

Dense twinning planes with deposition of boehmite along them are commonly found in corundum from India (48x)

Reflecting twinning planes (under cross polars) in labradorite feldspar from Bihar / Jharkhand (40x)

Yellow scapolite from Karur-Kangayam region in Tamil Nadu, India displaying brown zones caused due to exsolution of brown platelets (possibly lepidocrocite) along cleavage planes along the 'c' axis (top). These planes appear highly iridescent in reflected light (bottom) (top-48x; bottom- 64x)