This paper discusses the occurrences of gemstones, other than diamond, in eastern and southern India.

People are attracted to gemstones because of their transparency, clarity, brilliance, fire, durability, play of colours, amenability to cutting to give different shapes and because of their rare occurrences in the Nature. They are also adored because of the general faith in their influence on different zodiacs, in bringing good results in the life. This belief is very strong with the people of Asiatic countries. It is the art of the day for every jewellery shop to engage an astrologer to advise and guide people to wear particular types, and sizes of gems suitable for them.

Gemstone Belts of Eastern and Southern India
The states of Andhra Pradesh and Orissa of the eastern India and the state of Tamil Nadu in the southern India are the main locales of gemstone in India, other than Rajasthan. The gemstones in these parts of India are occurring in :

	Eastern Ghat Mobile Belt (EGMB), the gemstone tracts covering parts of Vizianagaram, Visakhapatnam and East Godavari districts of Andhra Pradesh and parts of Kalahandi, S. Koraput, Sambalpur, Bolangir, Phulbani and Dhenkanal districts of Orissa.
	Alkaline Complexes of Orissa.
	Alkaline Complexes of Andhra Pradesh.
	Alkaline Complexes of West Bengal.
	Granitic terrain of Tamil Nadu, consisting of high grade meta-petites, ultramafics, alkaline complexes and khondalites, traversed by pegmatites.
	Other Areas: Gemstones in minor quantity have also been reported from several districts of Karnataka and from Kerala also.

I. Eastern Ghat Mobile Belt (EGMB)
The contact zone of Eastern Ghat Mobile Belt (EGMB) with the Bastar Craton, bordering on south by river Godavari and on north by river Mahanadi, hosts the major gem tracts of eastern India. The main rocks of the EGMB belong to Khondalite Group, Charnockite Group, pyroxene granulites, migmatites and granitic gneisses. The rocks are subject to granulite facies of metamorphism. The main linear zones, hosting the resources of gemstones, are:

A. Racheruvalasa-Addatigala gemstone belt of Andhra Pradesh
The gemstone belt runs for a length of 250 km in the NE-SW direction from Racheruvalasa (close to Bobbili) in the Vizianagaram district on north to Addatigala in the East Godavari district on south. The belt hosts a number of known gemstone deposits, covering a width of 10 km.

Geologically, the belt is located in the north-central part of Eastern Ghat Mobile Belt. The gemstones mainly occur in both composite and zoned pegmatites, which have been emplaced in khondalite and migmatised khondalite. The contact zones of the khondalites with the porphyritic granitoid gneiss are the main loci for pegmatite-hosted gemstone mineralisation of this belt. The pegmatites are intrusive along the NE-SW trending linear fractures in the khondalites. The gemstone belt occupies the central part of the folded structure. The eastern and western limbs of the folded structure are sheared - the Sileru shear zone on the west and the Narsipatnam and Tuni-Eleswaram shear zones on the east.

Description of the gemstone belt:
The 100 km long gemstone belt hosts more than 100 gemstone occurrences. The main centre of gemstone occurrences is the tract between Gajapatinagaram in Araku Valley in Visakhapatnam district and Addatigala in the East Godavari district.

The main gemstone sectors of the belt are:

North to South
1. Racheruvalasa-Borra Sector, Vizianagaram-Visakhapatnam districts
This sector runs from Racheruvalasa of Vizianagaram district to Borra in Visakhapatnam district. In this sector, mica pegmatites have intruded calc-silicates, crystalline limestone and pyroxene granulites.

Racheruvalasa Area (near Bobbili)
Sillimanite cat’s eye occurs in pegmatites emplaced in khondalite.

Borra Area:
Gemstones like diopside, epidote, tourmaline, apatite and quartz are found in mica-pegmatites traversing calc-silicates, pyroxene granulite and crystalline limestone. Old workings have been located in Ninnimamidi, Koiteguda, Deccapadu, Kuntiasimidi and Bodilibadi for lepidolite and Lakshmipuram and Diguvasoba for tourmaline.

2. Araku Valley Sector, Visakhapatnam district
There is illegal mining by locals for yellowish green chrysoberyl cat’s eye (Vyduryam). Known occurrences are Turaiguda, Karaiguda, ITI, Sun-karametta, Burgulapadu, Korayi, Gunjriguda and Tudum. Gemstones are localised in quartzo-feldspathic aggregates in pegmatite, containing tourmaline, magnetite, zircon and sillimanite. Chrysoberyl occurs also in weathered / colluvial horizons at Tudum and Sunkarametta.

3. Munchingputtu-Machhupuram Sector, Vizianagaram district
Maximum number of occurrences are located around Paderu. Sillimanite cat’s eye is found in occurrences of Munchingputtu, Bakuru, Silakalaputtu, Sangam and Bokkedlu; yellowish chrysoberyl cat’s eye in occurrences of Mach-hipuram, Boddaputtu, Lingaputtu, God-ugurai, Biram, Gedelapadu, Solamaringi; both varieties in occurrences of Nittamamidi, Kottavuru, Godlapadu, Eguvasoba, Jogulaputtu, Borad-aputtu, Bodemela Colony, Sangam, Godugurai (the last 6 occurrences in a NE-SW trending closely spaced fracture system).

4. Chintapalle Sector, Visakhapatnam district
The gemstone occurrences are mostly located in reserve forest area. Good quality yellowish green and peacock green chrysoberyl cat’s eye and honey brown sillimanite cat’s eye occur in occurrences of Meduru, Pinapadu, Poturajuganula, Gurralagondi, Rintada and Satyavaram. Gemstones also occur in colluvium and soil.
There is illegal mining in pegmatites upto depths of 10m to 15m by making cross-adits or inclined shafts. Outcrops of pegmatite are scarce, but the pegmatites have depth persistence.

5. Addatigala Sector. East Godavari district
The gemstone occurrences are mostly located in Tapasikonda reserve forest. The pegmatites are emplaced in NE-SW trending closely spaced fracture systems in the highly folded khondalite. Alexandrite and good quality chrysoberyl cat’s eye occur in pegmatite occurrences of Sava-alagoyyi and Mampa near Koyyuru. Other important occurrences are Pandi Konda, Dup-pulapalem, Chipuru Konda, Vanarakshana Samithi and Paideputta.

6. Other Areas
Occurrences are located at the foothills and the plains close to the khondalites, having some economically potential occurrences of the gem tract.

Foothill occurrences: Kintalavallapuram*, Kute Kondalu, Pittagedda, Nittamamidi, Karaka, Sabbavaram*. Colluvium & Plains: Pappusettipalem*, Peddamadina*, Chintapaka*.

Chintapaka & Peddamadina Colluvials (weathered khondalite): Green & bluish green chrysoberyl cat’s eye and green alexandrite.

Pappusettipalem: Large quantity of yellow chrysoberyl cat’s eye.

Kintalavallapuram: Greyish blue chrysoberyl cat’s eye.

* = relatively most profitable blocks.

B. Gemstones in Eastern Ghat Granulitic Terrain of Orissa (part of EGMB)
The main gemstone tracts of the Granulitic terrain of Orissa are:
i) Sirjapalli - Tunda belt in Bhawanipatna/ Kalahandi districts.
ii) Muribahai-Tentil Kuntil belt in Bolangir district.
iii) Meghapal - Ranchipara belt in Sambalpur district.
iv) Paikadakalaguda - Hatamuniguda belt in Koraput district.

These belts occur in the western part of EGMB confined mainly to the khondalite suite of rocks and ultrabasics of the granulitic terrain. The important litho-units, which are the locales for gemstones, are high grade pelitic schists (mainly khondalites), ultramafics, calc-silicate rocks, anorthosites and potash granites. The pegmatites traversing these rocks form the main centres for search of gemstones.

The main locales are (i) emerald in vein quartz and pegmatite, traversing ultramafic schists in Kautabanj-Patnagarh area, Bolangir district, (ii) aquamarine in gneisses and mica-schists, traversed by pegmatite in Boudh-Phulbani area, (iii) ruby in cordierite-biotite rock in Jhilingdhar, Bhawanipatna, Kalahandi and Sambalpur districts, (iv) sapphire in garnetiferous amphibolite and garnet sillimanite-cordierite schists in Ganjam, Dhenkanal and Koraput districts, (v) garnet in high grade pelitic schists, anorthosites, meta-ultramafites and impure limestone traversed by pegmatites in Bhubaneswar, Koraput and Kalahandi districts. The other gemstones occurring in the granulitic terrain of Orissa are alexandrite, amethyst, chrysoberyl cat’s eye, heliodor, iolite, moonstone, rock crystal, rhodolite, topaz, tourmaline, zircon, amazonstone, chert, jasper, rose quartz and rhodonite.

II. GEMSTONES IN ALKALINE COMPLEXES OF ORISSA
Several alkaline rocks occur along the western and northern margins of the Eastern Ghats Mobile Belt (EGMB) in Orissa. The main centres are around Koraput, Khariar, Rairakhol, Kankrakhol-Lodhajhari and Baradangua. These alkaline complexes contain syenites, hornblende and biotite-bearing nepheline syenites, and rarely ultramafic alkaline rocks like ijolite, melteigite and malignite. These alkaline rocks host corundum, zircon, nepheline, nepheline cat’s eye, sapphire, beryl, amazonite (green microcline), sodalite etc.

The main centres are:
1. Baradangua Area
Detached bodies of syenites and nepheline syenites occur over a length of 1.50 km in WNW-ESE direction. The rocks host crystals of corundum and zircon, as is evident from the crystals found in the colluvial and alluvial zones around the rock outcrops. Most of the crystals are brownish and greyish brown in colour. Some grains are translucent and some are transparent. There are possibilities of finding sapphire and ruby.
2. Kankrakhol-Lodhajhari Syenite Belt:
At about 25 km WNW of Baradangua, occur 19 small lenses of syenites and nepheline syenites along a 32 km long NW-SE trending belt from Kankrakhol on north to Lodhajhari on south. Large crystals of nepheline, upto 12 cm, have been reported from nepheline syenites of this belt. There is scope of finding gem variety nepheline as well as corundum and zircon in view of reported occurrences of corundum and zircon from neighbouring syenites and nepheline syenites of Baradangua area.

3. Rairakhol Belt of Nepheline Syenite
Syenites occur along a 15 km long E-W trending belt from Kharsali on east to Kusarimunda on west near Rairakhol. Near Rairakhol, pegmatites/pegmatoidal syenites, intruded in khondalite, host beryl and zircon. This may be regarded as a prospective area for emerald, aquamarine and morganite in view of presence of beryl. Large crystals of pink and grey nepheline, upto 15 cm in diameter, also occur in nepheline syenites of this area. Some of the nepheline crystals show cat’s eye effect. Such large pink or flash red coloured nepheline crystals may form good gemstones under cabochon cut (Ghosh, 2001).

4. Khariar Alkaline Complex
The Khariar alkaline complex occurs along a 30 km long N-S trending belt of alkaline complex, which has been subjected to metamorphism developing gneissosity. The complex contains syenites, nepheline syenites, metagabbro, essexite, shonkinite and malignite. Alkali syenites occur along the eastern and western margins of the complex. Alkali granite also occurs at the border of the complex in the south-central part. This complex hosts sapphire, zircon, beryl and amazonstone. The syenites and the pegmatite-syenite composite bodies host semi-transparent to transparent gem variety sapphire, large crystals of which have been reported from the colluvial zones along the north-eastern margin of the Khariar alkaline complex (Karanth, 2000; Ghosh, 2001). The gem quality sapphire from this complex is ink blue to prussian blue in colour, transparent, free from inclusions and is amenable for faceting. Some star-grade stones are fairly large in size, exhibiting zoning and showing asterism.

Honey brown zircon has been reported from the southern part of this complex (Viswanatha, 1982; Ghosh, 2001). Ghosh et al (2001) has reported occurrences hosting large crystals of brown, honey brown and pinkish red zircons in colluvial/alluvial zones at about 750 m ENE of Sargigula and at 1.5 km NE of Putupara. Some crystals are more than 1.00 cm in length.

Along the western margin, several pegmatites, intruding the granitic gneisses, carry large crystals of amazonite (green microcline). Such a pegmatite vein of 10m x 2m was located by GSI south-east of Bodlapara which carries upto 15cm wide patches of parrot green amazonite. Another amazonite bearing peg-matite was found by GSI to the north-east of Keaburla.

A pegmatite, intrusive within granite gneiss, at 1.00km north-east of Putupara, hosts transparent bluish-green beryl, pinkish zircon and flesh-coloured feldspars.

Semi-transparent nepheline crystals, occurring as large crystals in nepheline syenites of the Khariar complex, are marketed as gemstones. Ghosh et al (2001) has reported the presence of sodalite in biotite nepheline syenite at about 1.00km north-west of Rokal.

Summing up, it may be said that the Khariar alkaline complex forms a potential target area for corundum, sapphire, zircon, amazonstone, beryl (including emerald), nepheline and sodalite. When sapphire occurs in this complex, it may be searched for ruby also.

III. GEMSTONES IN ALKALINE COMPLEXES OF ANDHRA PRADESH
A. Kunavaram alkaline complex
The largest alkaline complex of India occurs in the Khamman district of Andhra Pradesh, along the western margin of EGMB in close proximity of the Sabari-Silera Shear Zone (Mazumdar, et al 2000). The complex occurs between Kunavaram on north to Vinayakpuram on south.

Like the Khariar alkaline complex, the Kuna-varam complex also consists mainly of syenites and nepheline syenites, but unlike Khariar complex, some small bodies of carbonatites occurs here. The reported gemstones from this complex are:

i) Corundum & Sapphire
Semi-transparent to transparent sapphire occurs near Gummudupalle.
Large blue corundum crystals occur in composite syenite-pegmatite body along the eastern margin of the complex.

ii) Zircon
Large honey brown, brown and reddish- brown crystals of zircon have been reported from colluvial / alluvial zones, NNE of Vinayakpuram along the eastern margin of the complex.

iii) Nepheline
Large flesh-red nepheline crystals, upto 10 cm in length, occur in composite pegmatite-nepheline syenite bodies.

B. Kundulura alkaline complex
North-east of Kunavaram alkaline complex occurs two NE-SW trending bands of syenites and nepheline syenites near Kundulura. The reported gemstones are:

i) Corundum
Corundum crystals have been reported from the colluvials / alluvials along the western margin of the complex. Most of the crystals are brownish or greyish in colour, but some crystals are gem variety sapphire with deep blue colour.

ii) Nepheline
The composite pegmatite-nepheline syenite bodies host large pods and lenses of massive nepheline. On cutting, this may produce gem quality nepheline pendants.

IV. GEMSTONES IN ALKALINE COMPLEXES OF WEST BENGAL
Nepheline syenites and syenites occur in a E-W trending linear zone in Kusumda-Kankarkiyari area of Purulia district. This is the eastern continuation of North Purulia Shear Zone. The alkaline complex occurs as intrusives within the Chhotanagpur gneissic complex in association with granulites, garnet-sillimanite gneisses and amphibolites.

The reported gemstones are:

i) Corundum
Most of the corundum crystals, reported from colluvial zones close to alkaline rocks, are brown or greyish brown in colour, but some semi-transparent blue crystals, upto 5cm in length, have been reported; the transparency is less than that of gem quality sapphire. Blue corundum has also been reported from the pegmatite-syenite composite body along the southern margin of Kankarkiyari alkaline complex.

ii) Zircon
Some zircon crystals of honey-brown colour have been reported from colluvials of these alkaline rocks. A 100m x 50m colluvial zone occurs in Pirargoriya area which is rich in zircon crystals (Ghosh, 2001).

V. GEMSTONE OCCURRENCES IN TAMIL NADU
The Geological Survey of India, through intensified explorations, could locate a number of gemstone tracts in Tamil Nadu, a description of which was presented by Operation Tamil Nadu of GSI in GSI Special Publication No. 58, 2001. The synopsis is presented here:

General Guidelines in search for Gemstones in India

The generalised geological locations of gemstones in India are:

The above mentioned table presents generalised guidelines in the selection of host rock for searching different gemstones. This is just one of the aspects to be considered in search for gemstones. The pegmatites and pneumatolytic veins, genetically related with granitic emplacements, are the major carriers for thermal solutions which give birth to crystals of gemstones. And the easy passages for upward migration of the thermal solutions are the long continued fracture zones/ shears which have effective depth-continuity.

Combining all these issues, the following factors are to be considered as guidelines in search for gemstones:

1. Favourable geological milieu, as discussed above, specially the presence of pegmatites,        pneumatolytic veins and rocks of alkaline complexes and Al-rich meta-pelites like khondalite.
2.   Presence of granitic pluton in near-by locality.
3.   Presence of long-continued fractures / shears.
4.   Presence of favourable thermal aureoles.

The presence of granitic plutons, within or close to (i) Al-rich high grade meta-pelites which are traversed by pegmatites / zoned pegmatites or anorthosites and/or (ii) syenites and nepheline syenites and (iii) pegmatites traversing calc-silicates and crystalline limestone are ideal locales for searching for gemstones of Corundum Group, Beryl and Chrysoberyl Group, topaz, tourmaline, epidote, diopside, zircon, nepheline, amazonite, sodalite, sillimanite cat’s eye, spinel, sphene, kyanite, andalusite, apatite, iolite. Such geological environments, traversed by long continued fractures / shears in (i) Eastern Ghat Mobile Belt, (ii) South Indian granulitic belt, and (iii) the Gneissic complexes and Aravalli Supergroup of Rajasthan are the centres of prioritisation for search for gemstones.

The distribution of gemstones is mostly erratic in primary rocks. So, it is difficult to carry out any successful planned exploration for gemstones in primary rocks. Only large-scale operations over wide target areas may lead to success. But this creates environmental problems, especially in reserved / protected forest areas. So, the priority should be accorded to explore for easy targets like placer gemstones in streams, palaeo-channels, neo-gravel beds, colluvials etc.

Besides, while searching for gemstones, we can keep an eye for the following generalised gemstone associations (Singh, 2002):