mineral

Blue Glass or Slag Glass

Amorphous Silica (Anthropogenic Glass)

Hardness: 5-6 (Mohs scale), Color: Cobalt to light blue, Luster: Vitreous, Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific Gravity: ~2.4-2.8

Identified June 15, 2026More mineral →

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Physical properties

Hardness: 5-6 (Mohs scale), Color: Cobalt to light blue, Luster: Vitreous, Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific Gravity: ~2.4-2.8

Formation & geological history

Formed through the melting of silica with coloring agents (like cobalt or copper). While naturally occurring blue minerals exist, these specimens show distinctive curved conchoidal fracturing and bubbles characteristic of man-made glass waste or sea glass.

Uses & applications

Commonly used in decorative landscaping, aquarium gravel, bead making, or as 'sea glass' for jewelry and collecting when weathered by water.

Geological facts

Blue glass gets its color from transition metal oxides; cobalt oxide produces a deep blue, while copper or iron can produce lighter turquoise or aqua shades. It is often mistaken for gemstones like aquamarine or sapphire.

Field identification & locations

Identify in the field by looking for tiny air bubbles (vesicles), a lack of crystal faces, and a characteristic 'U' shaped or shell-like fracture pattern. Often found near old industrial sites or tidal beaches.

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mineral