mineral

Howlite

Calcium borosilicate hydroxide (Ca2B5SiO9(OH)5)

Hardness: 3.5 on Mohs scale; Color: Chalky white with dark grey or black spider-web veining; Luster: Sub-vitreous to earthy; Crystal structure: Monoclinic; Cleavage: None (conchoidal fracture); Specific Gravity: 2.45 to 2.58.

Hardness: 3
Color: Chalky white with dark grey or black spider-web veining
Luster: Sub-vitreous to earthy

Identified July 5, 2026More mineral →

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Physical properties

Formation & geological history

Formed in evaporite deposits, usually in arid environments or playa lakes. It occurs as nodules that resemble cauliflower heads. Most commercial deposits date from the Tertiary period.

Uses & applications

Commonly used for decorative carvings, lapidary work, and beads. Because of its porous nature, it is frequently dyed blue to imitate turquoise (often sold as 'turquenite') or red to imitate coral.

Geological facts

Howlite was first discovered in 1868 near Windsor, Nova Scotia, by Canadian mineralogist Henry How. While it looks like marble or turquoise, it is chemically related to borate minerals.

Field identification & locations

Collectors can identify it by its specific 'spider-web' matrix and chalky texture. It is softer than many other gemstones, meaning it can be scratched by a copper coin. Major locations include California (USA), Nova Scotia (Canada), and Turkey.

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Mineral

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Mineral/Rock

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