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Natural Glass

Snowflake Obsidian Rough, Natural Glass

Natural glass is formed naturally without the intervention of man. Its primary composition is silica with impurities. It (especially moldavite and snowflake obsidian) is used in carvings and beads.

Natural glasses are formed under different conditions and are basically made up of varying percentages of silica. The separation of natural glass from man-made glass is not possible with standard gemmological equipment. Obsidian, moldavite, crater glass and silica glass are variety of natural glass. The term Tektite has been used to represent all the natural glasses as a whole and also to define glasses of specific meteoritic origins.

Obsidian

1. Chemical Composition Varies, but 66% - 72% is silica
2. Colors / Varieties
  • Color: Black, grey, dark brown Transparency: Transparent to opaque.
  • Varieties: Rainbow obsidian with iridescent sheen; Flowering obsidian is black with white spherulitic inclusions.
3. Hardness 5
4. Specific Gravity 2.33 - 2.42
5. Optic Character Isotropic, S.R., A.D.R. (S.R.)
6. Refractive Index / Birefringence 1.48 - 1.52 / Nil.
7. Magnification Gas bubbles, crystallite inclusions which are round, rod-shaped or coiled, fine silky striations (cat's eye effect), color zoning and banding.
8. Geological Occurrence Formed by the rapid cooling of volcanic lava.
9. Sources Siberia, Mexico, Hungary, Hawaii, Japan, Iceland, Italy, U.S.A. (Nevada, Arizona - Yellowstone Park)

Moldavite

1. Chemical Composition Upto 75% silica, 10% alumina, with trace elements. Low water content (much lower than obsidian).
2. Colors / Varieties Bottle green, greenish brown, brown / Basically Tektites.
3. Hardness 5.5
4. Specific Gravity 2.30 - 2.40
5. Optic Character Isotropic, S.R., A.D.R. (S.R.)
6. Refractive Index / Birefringence 1.49 - 1.51
7. Magnification Gas bubbles, swirl marks which are thick, very different from pastes. Total lack of crystallites.
8. Geological Occurrence Meteoritic zones.
9. Sources Bohemia, Czech Republic, Peru, Ivory Coast of Africa, Australia, Malay Archipelago.

Crater Glass

1. Chemical Composition Commonly fused silica (90%) with some impurities.
2. Colors / Varieties Greenish yellow, black.
3. Specific Gravity 2.10 - 2.30
4. Optic Character Isotropic, S.R., A.D.R. (S.R.)
5. Refractive Index / Birefringence 1.46 - 1.54
6. Magnification Numerous vesicles present (S.G. lower than other natural glasses).
7. Geological Occurrence Meteoritic zones.
8. Sources Germany, U.S.A. (Arizona), Central Australia, Saudi Arabia.

Silica Glass

1. Chemical Composition Pure silica (upto 98%)
2. Colors / Varieties Greenish yellow is common, black.
3. Hardness 6
4. Specific Gravity 2.20 - 2.50
5. Optic Character Isotropic, S.R., A.D.R. (S.R.)
6. Refractive Index / Birefringence 1.46 - 1.52
7. Sources Sandy deserts of Libya, Arabia, India (Rajasthan).
  • When a lightning bolt strikes the ground, thin tubes of fused sand are formed due to intense heat build-up. Fulgarite is the name given to such fused sand glasses.
  • Non-volcanic, extra terrestrial glass of meteoric origin is called a Tektite. Tektites are mostly found in Czech Republic, Australia, South-East Asia, West Africa, U.S.A. (Georgia - Texas).
  • In general, all natural glasses are sometimes clubbed together as Tektites.

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In Rome, a talisman having coral pieces is considered very auspicious to quell the bad spells of evil look. The Romans were in the habit of hanging chains made of ancient coral pieces from the cradle of the infants to protect them from evil effects.

In China, people wear rings studded with tiny conch or oyster shells as they believe it cures all aches such as stomach ache, worms and like.

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It is believed that a turquoise gifted to a friend or a lover turns his or her life into one of happiness and good luck.

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