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by gagan choudhary

Inclusions in Indian Rubies

by 

Gagan Choudhary

Shyamala Fernandes

Note: This paper is an extension of the paper titled, "Indian Ruby - Deposits & Characterisation" authored by Shyamala Fernandes, Vikas Joshi, Dr. Dietmar Schwarz and Ritu Bharadwaj, presented at the International Gemmological Conference (IGC), held in Goa in 1999. While, the current study was presented at the International Gemmological Conference (IGC) held in Vietnam in October 2013. In this paper, the emphasis has been given on the inclusions rather than the characterisation of the material.     

INTRODUCTION

India is known to produce exquisite blue sapphires from Kashmir, along with some extraordinary sizes of star rubies from Mysore in the Karnataka state and facet-grade rubies and pink sapphires from Karur district of Tamil Nadu (e.g. Fernandes et al., 1999 and Durlabhji et al., 2003).


Ruby deposits in India are located in the following states (Fernandes & Choudhary, 2010), which are mainly being worked out by local villagers:

  • Tamil Nadu: Karur, Salem, Manvadi, Kambam, Coimbatore, Madurai and Tiruchirapalli
  • Andhra Pradesh: Khammam, Guntur, Anantpur, Warangal, Vishakhapatnam and Hyderabad
  • Karnataka: Mysore, Ramannahalli, Coorg, Mercara, Tumkur, Hassan and Chikmangalur
  • Chhattisgarh: Raipur and Bastar
  • Odisha (Orissa): Kalahandi and Bolangir
  • Maharashtra: Bhandara (e.g. Indian Bureau of Mines, 2010)

Figure 1: Map of India showing major ruby deposits

Ruby deposits in India are mainly associated with gneisses and schists, with variations in mineralogical composition and grade of metamorphism (see e.g. Sarkar & Guru, 2005). The basic rock types have been given in table 1.


In this paper, an attempt has been made to correlate the types of inclusions observed in rubies from various Indian states and their associated rock types.


MATERIALS and METHODS

Studied samples

77 specimens - 55 rough and 22 fashioned (faceted as well as cabochons - with and without star)

One face of 25 rough samples out of 55 were polished for the purpose of inclusion study. These were collected directly from the miners.


Equipment used

Optical (gemmological) microscope with various types of illuminations

Airix Corporation / TechnoS Instruments' STR 300 confocal microspectrometer with solid state 532 nm laser excitation; exposure time - 10 seconds per scan, and 10 scans per target.

Shimadzu IR Prestige 21 FTIR with diffused reflectance accessory at resolution of 4 cm-1 and 50 scans per sample.

Figure 2: Representative samples of rough and cut rubies from various Indian sources


RESULTS and DISCUSSION

The common inclusions observed in Indian rubies are illustrated as follows and their association with the rock types are summarised in Table 1.















Anatase

Euhedral - Prismatic

Chhattisgarh

























Apatite 

Euhedral - Prismatic 

Tamil Nadu

(80x)



























Apatite 

Anhedral – Conical 

Orissa

(80x)
























Diaspore 

Euhedral – Subhedral 

Chhattisgarh

(80x)


























Feldspar 

Rounded – Elongated 

Chhattisgarh




























Hematite 

Sub-hexagonal - Platy 

Chhattisgarh

(80x)

























Monazite 

Euhedral – Bipyramidal 

Tamil Nadu



























Muscovite 

Euhedral- Platy 

Karnataka
























Phlogopite 

Euhedral- Prismatic 

Tamil Nadu

(80x)

























Pyrrohtite 

Subhedral- Prismatic 

Karnataka
(80x) 


























Rutile 

Euhedral – Prismatic 

Tamil Nadu

(64x)



























Rutile 

Anhedral

Tamil Nadu

(80x)

























Spinel

Grains

Orissa

(80x)

























Zircon 

Euhedral - Prismatic- Pyramidal

Tamil Nadu


























Zircon 

Euhedral - Prismatic

Tamil Nadu


























Three directional long and short rutile silk intersecting at 60/120 degrees, oriented along the basal plane

(80x)



























Boehmite 

Films – along twin planes 

Andhra Pradesh

(48x)

























Negative crystal with elongated diaspore

Chhattisgarh





























Phase inclusion with CO2 bubble

Chhattisgarh





















Growth / Colour zoning with or without zones of rutile dust / discs / needles (48x)











TABLE 1:  Common types of inclusions observed in Indian rubies and their associated rock types

Click to edit table header
 
 
 
 
SOLID INCLUSIONS
(CRYSTALS)
Study by Fernandes et al, 1999
  SOLID INCLUSIONS
(CRYSTALS)
This Study
  ROCK TYPE
[Fernandes et al., (1999); Panjikar J. (1997, 1999, 2002)]
  TAMIL NADU

Rutile

(Unidentified) colourless, transparent, rounded to prismatic crystals
 Apatite

 Monazite (yellowish,  bipyramidal)

 Phlogopite (yellowish,  elongated and tabular)

 Rutile (brown, euhedral to  sub-rounded)

 Zircon (colourless, elongated  and rounded, with stress)
  Basic holocrystalline granitoid gneiss with orthopyroxene   (charnockites)
  KARNATAKA
Rutile (orangy-brown / black, rounded - elongated, metallic lustre) 
 Muscovite (gray, tabular,  sub- hedral)

 Nepheline (black, elongated,  euhedral)

 Pyrrohtite (black, tabular,  sub- rounded)

 Rutile (brown, euhedral  to sub- rounded to anhedral)
  Contact zones of ultramafic rocks and pegmatite veins,   within pelitic schists; gabbroic anorthosite, permeated by   magnesite  
 ANDHRA PRADESH
None
 Rutile (brown, sub rounded  to  anhedral)
 Zircon (black, rounded with  metallic lustre)
  Quartz, feldspar, mica, hornblende and sillimanite rich         gneiss and schists, along with nepheline, corundum and     zircon syenites  
 ODISHA (ORISSA)
(Unidentified) colourless, transparent, rounded to prismatic crystals

 Apatite (colourless, euhedral  to  anhedral)

 Muscovite (gray, platy, sub-  hedral)

 Spinel (black, sub-rounded)  
  Highly foliated gneiss, closely associated with schists of     variable composition; rich in plagioclase feldspar.               Corundum occurs along the contact of the gneiss and         limestone. Another rock type is gneiss and slillimanite         schist (khondalite)
 CHHATTISGARH
 

Rutile (orangy brown, rounded)

Pyrite (golden yellow, rounded)

(Unidentified) colourless, transparent crystals

(Unidentified) greenish brown crystals
 

 Anatase (brown, elongated,  platy)

 Apatite (white, sub-hedral to  rounded)

 Diaspore (white, frosty,  elongated, bipyramidal)

 Feldspar (colourless,  rounded)

 Hematite (black, metallic,  platy, elongated)

 Muscovite (colourless,  sub- hexagonal)

 Rutile (anhedral and flaky)

 Zircon (colourless,  elongated,  bipyramidal)
Highly foliated gneiss, closely associated with schists of     variable composition; rich in plagioclase feldspar.               Corundum occurs along the contact of the gneiss and         limestone. Another rock type is gneiss and slillimanite         schist (khondalite)  

In addition to the above listed solid (crystal) inclusions, Indian rubies also displayed a variety of inclusions in this study, which are listed below:


Exsolved inclusions:

  • Long and short three-directional (rutile) silk; short silk with re-entrant angles at the broader end
  • Iridescent discs / dust concentrated along the hexagonal zones / bands
  • Whitish needles (boehmite) along the edges of twinning planes
  • Whitish films (boehmite / diaspore) along the surface of twinning planes (appear iridescent in reflected light)


Fingerprints: In the form of veils, however, their visibility is not very pronounced, due to the presence of large number of twinning planes.


Negative Crystal / phase: Three phase containing CO2 & diaspore crystal


Growth / Colour Zoning: Very common in most of the rubies (especially the star varieties) forming hexagonal to pseudo-hexagonal patterns; these zones typically contain rutile discs, dust, and / or short needles


Twin Planes: With intervals varying from very dense to broad


Others: Iron stained fractures / films are commonly present in rubies from most of the deposits


CONCLUSIONS

This study revealed a wide range of inclusions found in Indian rubies, which were of more or less similar type, pattern and appearance. No consistency was observed in the type and pattern of inclusion, restricted to a specific locality (states) and the associated rock types, although some of the mineral inclusions were identified only in specific locality such as hematite and anatase (in Chhattisgarh), black spinel (in Orissa), pyrrohtite and nepheline (in Karnataka) and monazite (in Tamil Nadu).


REFERENCES

Choudhary, G., 2012. An overview of inclusions in Indian gemstones. 3rd International Gem & Jewelry Conference (GIT 2012),Bangkok, proceeding volume, pp 149- 152.

Durlabhji, M., Fernandes, S., Choudhary, G., 2003. ICA Mining Report.

Fernandes, S., Joshi, V., Schwarz, D. & Bharadwaj, R., 1999. Indian Ruby - Deposits & Characterization. XXVI International Gemmological Conference, Goa, India.

Fernandes, S. & Choudhary, G., 2010. Understanding Rough Gemstones. Indian Institute of Jewellery, Mumbai.

Indian Bureau of Mines 2010. Indian Minerals Year Book 2011, 50th ed. Indian Bureau of Mines, Nagpur, India (http://ibm.nic.in/IMYB%202011_Corundum%20&%20Sapphire.pdf; accessed 03-05-2013).

Panjikar, J., 1997. Comparative study of corundum from various Indian occurrences - Corundum from Orissa. Indian Gemmologist, 7(1-2), 12 – 17.

Panjikar, J., 1999. Comparative study of corundum from various Indian occurrences - Corundum from Karnataka. Indian Gemmologist, 8(1-2), 3-8.

Panjikar, J., 2002. Comparative study of corundum from various Indian occurrences - Corundum from Tamil Nadu. Indian Gemmologist, 10(1-2), 3-8.

Sarkar, S.K. & Guru, A.I., 2005. Review of gemstone belts of eastern and southern India and guidelines for the search of gemstone deposits. Indian Gemmologist, 13(1-2), 41-49.