mineral
Howlite
Calcium borosilicate hydroxide (Ca2B5SiO9(OH)5)
Hardness: 3.5 on Mohs scale; Color: Milky white to grey with dark grey or black veins; Luster: Sub-vitreous to pearly; Crystal structure: Monoclinic; Cleavage: None (conchoidal fracture); Opaque.
- Hardness
- 3
- Color
- Milky white to grey with dark grey or black veins
- Luster
- Sub-vitreous to pearly
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Physical properties
Hardness: 3.5 on Mohs scale; Color: Milky white to grey with dark grey or black veins; Luster: Sub-vitreous to pearly; Crystal structure: Monoclinic; Cleavage: None (conchoidal fracture); Opaque.
Formation & geological history
Formed in evaporite deposits, usually found in nodules that look like cauliflower heads. It is a borate mineral often found in arid climates like the Mojave Desert.
Uses & applications
Primarily used for decorative carvings, jewelry, and beads. It is frequently dyed blue to imitate turquoise or red to imitate coral.
Geological facts
Howlite is naturally very porous, which makes it an ideal candidate for dyeing. It was first discovered in 1868 by Henry How in Nova Scotia, Canada.
Field identification & locations
Identified by its white porcelain-like appearance and spider-web dark veining. To distinguish it from magnesite, a chemical test for boron can be used. It is soft enough to be scratched by a copper coin.
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