Man-made Glass (Not a natural rock or mineral)

Green Glass Cullet / Recycled Glass

Amorphous Silicon Dioxide (SiO2) with various metal oxides

Hardness: Roughly 5
Luster: Vitreous (glassy)

Identified July 18, 2025More man-made glass (not a natural rock or mineral) →

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Physical properties

Hardness: Roughly 5.5-6.5 on Mohs scale (similar to quartz). Color: Varying shades of green due to intentional colorants or iron impurities in recycling. Luster: Vitreous (glassy). Crystal Structure: Amorphous (lacks a defined crystal structure). Cleavage: Conchoidal fracture (smooth, curved breaks, like the inside of a seashell). Specific Gravity: Approximately 2.4-2.8.

Formation & geological history

This material is not naturally occurring; it is industrial or recycled glass. It forms when raw materials (primarily silica sand, soda ash, and limestone) are melted at high temperatures (around 1700°C) and then cooled rapidly, preventing crystal formation. The green color often comes from additives (like chromium oxides) or iron impurities in recycled glass. Its 'geological age' is recent, tied to human industrial activity, not geological processes.

Uses & applications

Commonly used as decorative landscaping material, fire pit glass, gabion fill, or as a raw material for remelting into new glass products. It is not used in jewelry as a gemstone but can be incorporated into craft items. It is not a construction aggregate in the traditional sense but can be used in permeable paving systems or recycled concrete.

Geological facts

This material is commonly referred to as 'slag glass' or 'cullet' when used in decorative applications, though it's typically just recycled glass. While natural glass like obsidian forms from volcanic activity, this material is clearly manufactured. The term 'sea glass' is often used for naturally tumbled pieces of similar material found on beaches.

Field identification & locations

In the field (or rather, in a pile of material), it's identified by its completely amorphous texture, conchoidal fracture, and often, the presence of bubbles or flow lines characteristic of manufactured glass. Unlike natural minerals, it won't show crystal faces or typical mineral cleavage. Common locations where it's 'found' are recycling centers, demolition sites, landscaping supply yards, or areas where industrial glass has been discarded. It has no collecting value as a geological specimen, but some may collect unusual colors or antique glass pieces.

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Man-made Synthetic Material (Plastic/Composite)

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Non-geological / Synthetic

Opalite (Man-made Glass)

Synthetic Opalised Glass

mineral