mineral

Howlite

Calcium Borosilicate Hydroxide (Ca2B5SiO9(OH)5)

Hardness: 3.5 (Mohs), Color: Milk-white to grey with dark spider-web veins, Luster: Sub-vitreous to earthy, Structure: Monoclinic, Cleavage: None/Indistinct, Specific Gravity: 2.53-2.59

Hardness: 3

Identified March 27, 2026More mineral →

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Physical properties

Hardness: 3.5 (Mohs), Color: Milk-white to grey with dark spider-web veins, Luster: Sub-vitreous to earthy, Structure: Monoclinic, Cleavage: None/Indistinct, Specific Gravity: 2.53-2.59

Formation & geological history

Formed in evaporite deposits, typically found in arid environments associated with borate minerals. Most specimens are derived from deposits in Canada and the United States (California) dating to the Tertiary period.

Uses & applications

Primarily used in jewelry for decorative beads and carvings. In industry, it is a minor source of borate. It is frequently dyed blue to imitate turquoise or red to imitate coral.

Geological facts

Howlite was discovered in 1868 near Windsor, Nova Scotia, by Canadian mineralogist Henry How. Because of its porous nature, it is one of the most commonly dyed minerals in the gemstone market.

Field identification & locations

Identified in the field by its characteristic greyish veins (matrix) and low hardness (can be scratched by a copper coin). Found in nodular masses resembling cauliflower. Common locations include Tick Canyon, California and Nova Scotia, Canada.

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