Mineral

Howlite

Calcium borosilicate hydroxide (Ca2B5SiO9(OH)5)

Hardness: 3.5 on Mohs scale; Color: Opaque white or grey with dark grey, black, or brown veins; Luster: Sub-vitreous to dull; Crystal structure: Monoclinic; Cleavage: None; Specific Gravity: 2.45 to 2.58.

Hardness: 3
Color: Opaque white or grey with dark grey, black, or brown veins
Luster: Sub-vitreous to dull

Identified January 11, 2026More mineral →

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Physical properties

Formation & geological history

Formed in evaporite deposits, usually as nodules in sedimentary environments like salt basins. It is often found associated with other borate minerals. Most deposits are relatively young in geological terms, often Cenozoic.

Uses & applications

Primary use is in jewelry and decorative carvings. Due to its porous nature and white color, it is frequently dyed blue to imitate turquoise or red to imitate coral. It is also used as a minor source of borate.

Geological facts

Howlite was first discovered in Nova Scotia by Henry How in 1868. It is famous for its 'matrix' of dark veins which gives it a cobweb-like appearance similar to high-grade turquoise.

Field identification & locations

Identify in the field by its distinct white color, cauliflower-like nodule shape (when unpolished), and dark erratic veining. Common locations include Tick Canyon, California, and various sites in Nova Scotia, Canada. Collectors should note it is much softer than quartz or turquoise.

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