mineral
Howlite
Calcium borosilicate hydroxide (Ca2B5SiO9(OH)5)
Hardness: 3.5 on Mohs scale; Color: White to milky white with grey or black veins; Luster: Sub-vitreous to pearly; Crystal structure: Monoclinic; Cleavage: None; Specific gravity: 2.53-2.59
- Hardness
- 3
- Color
- White to milky white with grey or black veins
- Luster
- Sub-vitreous to pearly
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Physical properties
Hardness: 3.5 on Mohs scale; Color: White to milky white with grey or black veins; 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, typically associated with nodules in borate deposits. Found in Canada, USA (California), and Germany.
Uses & applications
Used primarily in jewelry as beads or cabochons. Frequently dyed blue to imitate turquoise or red to imitate coral. Also used for carvings and decorative items.
Geological facts
Named after Henry How, a Canadian mineralogist who first described it in 1868. Because of its porosity, it is the most common mineral used to create imitation turquoise.
Field identification & locations
Identified in the field by its distinctive 'cauliflower' nodule shape and grey spider-web veining. It is much softer than quartz and can be scratched with a copper coin.
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metamorphic
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