mineral
Howlite
Hydrated calcium boro-silicate (Ca2B5SiO9(OH)5)
Mohs hardness of 3.5, white or milky color often with dark grey or black web-like veins (matrix), sub-vitreous to earthy luster, monoclinic crystal system (though crystals are extremely rare; usually found as massive nodules), no visible cleavage.
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Physical properties
Mohs hardness of 3.5, white or milky color often with dark grey or black web-like veins (matrix), sub-vitreous to earthy luster, monoclinic crystal system (though crystals are extremely rare; usually found as massive nodules), no visible cleavage.
Formation & geological history
Forms in evaporite deposits, typically in borate-rich playa lakes or basins through the chemical precipitation of evaporating waters. Geological age varies depending on the deposit, mostly Cenozoic.
Uses & applications
Commonly used for ornamental objects, carvings, beads, and cabochons in jewelry. Because it is porous, it is frequently dyed blue or green to imitate turquoise or lapis lazuli (sometimes sold as 'turquenite').
Geological facts
Howlite was first discovered in Nova Scotia, Canada, in 1868 by Henry How, a Canadian chemist, geologist, and mineralogist.
Field identification & locations
Easily identified by its chalky-to-porcelain white surface and characteristic dark webbed matrix. It is quite soft and can be easily scratched by a knife or copper coin. Found notably in Canada, the USA (California), and South Africa.
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