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5 - 6½
From the Celtic word "glas" ("bluish-green")
An amorphous, homogeneous material with a random liquid-like structure generally formed due to rapid cooling.
Glasses can be natural rocktypes (such as obsidian, lechatelierite or tektite) or artificial materials (e.g., in slags). Most natural and artificial glasses are predominantly composed of silica with variable amounts of impurities, especially alkalis.

Crystals in volcanic rocks may contain tiny inclusions of frozen melt, i.e., glass.

In gemmology, man-made glasses have been used as gems since the invention of glass manufacture, and special glass varieties, such as lead glass, containing additives have been used to simulate more valuable gemstones, such as diamond.

Visit for gemological information about Glass.

Classification of Glass

Physical Properties of Glass

Diaphaneity (Transparency):
Transparent, Translucent, Opaque
Hardness (Mohs):
5 - 6½
Hardness Data:

Other Names for Glass

Name in Other Languages:
Simplified Chinese:玻璃

Other Information

Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

Glass in petrology

An essential component of (items highlighted in red)

Internet Links for Glass URL:
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The following Glass specimens are currently listed for sale on

Localities for Glass

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