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Chemical Formula | Ca2B5SiO9(OH)5 | ||
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Composition | Basic calcium silico-borate | ||
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Color | White, commonly marked with black or brown intersecting vine-like or skin-like veins | ||
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Streak | White | ||
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Hardness | 3½ | ||
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Crystal Forms and Aggregates |
(Monoclinic) Occurs in giant masses and as fragments of them. Also occurs as large and small nodules resembling cauliflower heads. Large masses have the same texture as unglazed porcelain. Crystals, which are tabular, are barely noticeable with the naked eye. They are found in only one locality (Nova Scotia), where the crystals occur on large nodules. Also occurs scaly and earthy. | ||
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Transparency | Translucent in thin splinters; otherwise opaque | ||
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Specific Gravity | 2.5 - 2.6 | ||
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Luster | Dull, sometimes vitreous | ||
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Cleavage | None | ||
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Fracture | Conchoidal to even | ||
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Tenacity | Brittle | ||
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Other ID Marks | Occasionally fluoresces cream-yellow to white in shortwave ultraviolet light | ||
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In Group | Borates ; Hydrous borates. Contains silicon and oxygen, and is therefore regarded as a silicate [nesosilicate] by some. |
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Uses | The attractive black and brown intersecting veins in many Howlite specimens make it useful as an ornamental stone. Many masses and nodules are tumbled and polished, then sold to collectors, who find a particular liking to this inexpensive stone. Howlite is easily dyed, and if dyed turquoise-blue it resembles the mineral Turquoise. In fact, Howlite is used as a cheap substitute for Turquoise. Some dealers dishonestly label dyed Howlite as Turquoise. | ||
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Striking Features | Mineral structure and localities | ||
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Complex Tests | Soluble in hydrochloric acid | ||
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Popularity (1-4) | 3 | ||
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Prevalence (1-3) | 2 | ||
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Demand (1-3) | 2 | ||
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Distinguishing Similar Minerals |
Datolite - harder (5 -
5½), different mode of occurrence Bakerite - harder (4½) |
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Commonly Occurs With |
Borax, Ulexite, Colemanite, (Clay) | ||
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Noteworthy Localities |
Howlite occurs at many evaporation deposits in southern California as huge nodules. Notable areas include Lang, Los Angeles Co.; Tick Canyon (near Saugus), Los Angeles Co.; Dagget, San Bernardino Co.; and Death Valley, Inyo Co. It also occurs in the Bras D'Or lake off Cape Breton Island, Nova Scotia, Canada. Another locality in Nova Scotia, near Windsor in Hants Co., is famous for its tiny tabular crystals on large nodules. It the only locality to date where crystallized examples of this mineral occur. | ||
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Picture Icon Links |
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Picture Links | 1. Polished Howlite |
