mineral

Howlite

Calcium borosilicate hydroxide (Ca2B5SiO9(OH)5)

Hardness: 3.5 on Mohs scale; Color: Milky white to grey with dark grey or black veining; Luster: Sub-vitreous to pearly; Crystal structure: Monoclinic; Cleavage: None; Specific gravity: 2.53-2.59

Hardness: 3
Color: Milky white to grey with dark grey or black veining
Luster: Sub-vitreous to pearly

Identified May 7, 2026More mineral →

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Physical properties

Hardness: 3.5 on Mohs scale; Color: Milky white to grey with dark grey or black veining; Luster: Sub-vitreous to pearly; Crystal structure: Monoclinic; Cleavage: None; Specific gravity: 2.53-2.59

Formation & geological history

Formed in evaporite deposits within sedimentary basins, often alongside other borate minerals like ulexite or colemanite. It results from the crystallization of boron-rich groundwater.

Uses & applications

Primary use is in the creation of decorative objects, beads, and carvings. Because it is highly porous, it is frequently dyed blue to imitate turquoise or red to imitate coral.

Geological facts

First discovered by Henry How in 1868 near Windsor, Nova Scotia. In its natural form, it often occurs as irregular nodules resembling a cauliflower.

Field identification & locations

Can be identified in the field by its characteristic 'webbed' or dendritic black/grey veining over a white base. Unlike turquoise, it is very soft and can be scratched with a copper penny.

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