Obsidian is a mineral with a hardness of 5 out of 10 on the Mohs scale of mineral hardness [?]. These Amorphously structured gems are made of silicon dioxide, their full chemical compound being SiO2.

Obsidian is an extrusive igneous rock, a volcanic glass formed by rapid cooling.

Its essential component is glass. Its accessory components are magnetite, ilmenite, oxides and other minerals, such as feldspar.

It has the same composition as dacite or rhyolite, with less than 1 percent water.

Its color is shiny black, with clear conchoidal (shell-like)fracture, its texture glassy with rare microphenocrysts and abundant opaque fine dust scattered in concentric zones.

The black color appears because of the way the embryonic crystals in the glass scatter the light. Varieties show golden or silver sheen caused by inclusions.

Obsidian may also be red-brown due to the presence of iron, and greenish or grey due to the presence of tiny gas bubbles.

It has a massive structure, with, in some cases, the presence of latent concentric fractures (perlitic fractures).

Obsidian is derived from the rapid cooling of a viscous, granitic magma. It is found as volcanic units, as fragments thrown into the air by erupting volcanos, sometimes as long filaments ("Pele's hair") and as the outer covering of rhyolitic and dacitic domes .

It is not widely distributed, although it is the commonest of natural glasses. But it is very common in recent lava flows. mostly from felsic volcanos (Japan, Java). It is found in the tertiary lavas of the Lipari Isles (Italy). The most striking occurrence is in Obsidian Cliff in Yellowstone National Park, Wyoming (USA). It is also found in Hungary and Iceland.

The specific gravity [?] for Obsidian is 2.35, it's refractive index [?] is 1.48-1.51, and it's double refraction [?] is None.

History

Obsidian is named after a Roman, "Obsius."


Shattered fragments of obsidian have sharp edges high vitreous luster, and was used in prehistoric times and antiquity for tools and sculptures.

Industrial Usages

It is currently used industrially as raw material for rock wool.


Especially prized are such varieties as snow-flake obsidian, which contains small, grey spherullites, and the silky lustred obsidian of Mexico.

You May Also Like...

Tektites

Tektites: Tektites are glass specimens rich in silica that many believed were actually meteorites. But, the locations in which tektites have been found, and their chemistry, led scientists to suggest that they may not in fact have come from outside planet Earth. Another conjecture is that tektites are formed from rocks that melted after being hit by a meteorite. Tektites actually have a composition not unl (read full)

Onyx

Onyx: Onyx is a translucent to semitransparent variety of Agate, which in turn is a variety of Chalcedony or cryptocrystalline quartz that is porous and consists of straight or parallel banded agate of alternating shades of milky white and black, gray and black, black and red, white and red, white and brown. The term onyx has been erroneously applied as a suffix to Brazilian onyx, Mexican onyx, Orient (read full)

Tags

obsidianvolcanicglassextrusiveigneousrockblackironpeles hairobsiusrock woolsnow flake obsidiansilicon dioxide

Terms

Double Refraction or dr is the ability of a mineral to separate a refracted ray of light into 2 rays. If held over an image or text it will display the object 2x its original size.

Mohs Scale of Mineral Hardness is the standard used to categorize a mineral's ability to resist scratching. It gets its name from Friedrich Mohs, the German geologist who first created the scale.

RI or Refractive Index defines light's ability to move through the mineral or in a general sense, any material.

SG or Specific Gravity is the ratio of the weight of any substance to that of pure water at temperature of 3.98°C(39.2°F) and standard atmospheric pressure. This is important to note when actively seeking these minerals in the wild. Minerals with a higher SG will settle below material with a lower sg over time.