Rock Identifier
Sea Glass (Cobalt Blue) (Amorphous Silica (Glass with Cobalt additives)) — Anthropogenic specimen (man-made)
Anthropogenic specimen (man-made)

Sea Glass (Cobalt Blue)

Amorphous Silica (Glass with Cobalt additives)

Hardness: 5.5-6 (Mohs scale); Color: Intense cobalt blue; Luster: Frosted/Vitreous; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Surface: Pitted and hydrated due to saltwater exposure.

Hardness
5
Color
Intense cobalt blue
Luster
Frosted/Vitreous
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Physical properties

Hardness: 5.5-6 (Mohs scale); Color: Intense cobalt blue; Luster: Frosted/Vitreous; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Surface: Pitted and hydrated due to saltwater exposure.

Formation & geological history

Formed from discarded glass bottles or jars. Over 20 to 100 years, the glass undergoes physical weathering by ocean waves and chemical weathering (hydration and leaching) in saltwater environments.

Uses & applications

Used primarily in jewelry making, coastal decor, mosaic art, and as a popular beachcomber's collectible.

Geological facts

Cobalt blue sea glass is known as 'The Sapphire of the Beach.' It often originates from 19th and early 20th-century medicine bottles, such as Bromo-Seltzer, Noxzema, or Vicks VapoRub jars.

Field identification & locations

Identify by its frosted, 'C'-shaped pitted texture and rounded edges. Unlike craft glass, genuine sea glass should not have sharp edges or a shiny surface. Commonly found on rocky or high-energy shorelines near historic dumping sites.

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