mineral

Howlite

Calcium borosilicate hydroxide (Ca2B5SiO9(OH)5)

Hardness: 3.5 on Mohs scale; Color: White to milky grey with black or brown veining; Luster: Sub-vitreous to dull; Crystal structure: Monoclinic; Cleavage: None; Specific gravity: 2.53-2.59

Hardness: 3
Color: White to milky grey with black or brown veining
Luster: Sub-vitreous to dull

Identified June 7, 2026More mineral →

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Physical properties

Hardness: 3.5 on Mohs scale; Color: White to milky grey with black or brown veining; Luster: Sub-vitreous to dull; Crystal structure: Monoclinic; Cleavage: None; Specific gravity: 2.53-2.59

Formation & geological history

Formed in evaporite deposits within sedimentary basins through the precipitation of boron and silicate minerals from saline solutions, typically in arid environments during the Cenozoic era.

Uses & applications

Commonly used as a decorative stone in jewelry (beads, cabochons) and as a base material for imitation turquoise or lapis lazuli due to its porous nature. Also used as a minor source of borate.

Geological facts

Named after Henry How, a 19th-century Canadian mineralogist who first described it in Nova Scotia in 1868. It is naturally rarely found in crystal form, usually appearing in 'cauliflower' nodules.

Field identification & locations

Identified by its distinctive white color and dark, spider-web veining. It is quite soft and can be easily scratched by a steel knife. Major localities include California, USA and Nova Scotia, Canada.

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