mineral

Glendonite (Calcite Pseudomorph after Ikaite)

Calcite (CaCO3) pseudomorph after Ikaite (CaCO3·6H2O)

AI-generated identification · may be incorrect

Hardness: 3 (calcite); Color: Tan, brown, or grey; Luster: Dull to vitreous; Crystal structure: Originally monoclinic (ikaite), now trigonal (calcite); Specific Gravity: 2.71.

Hardness: 3 (calcite)
Color: Tan, brown, or grey
Luster: Dull to vitreous

Identified July 19, 2026More mineral →

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Physical properties

Hardness: 3 (calcite); Color: Tan, brown, or grey; Luster: Dull to vitreous; Crystal structure: Originally monoclinic (ikaite), now trigonal (calcite); Specific Gravity: 2.71.

Formation & geological history

Formed as ikaite crystals in cold, organic-rich marine sediments near freezing temperatures. As temperatures rise above 8°C, the ikaite becomes unstable and dehydrates into calcium carbonate (calcite), preserving the original spiked crystal shape.

Uses & applications

Primarily a collector's specimen and geological indicator of ancient cold-water environments (paleoclimatology).

Geological facts

Glendonites are named after Glendon, Australia, where they were first described. They are often called 'pineapple opals' when replaced by opal, or simply 'cold-water indicators' by geologists.

Field identification & locations

Identify by its distinctive stellate, spiked, or 'hedgehog' globular form. Often found in shales or mudstones that represent ancient glacial or deep-sea marine environments.