Howlite is a calcium borosilicate mineral. The mineral’s existence is directly tied to specific geological conditions rich in boron, a relatively uncommon element in the Earth’s crust. Understanding the origin of howlite requires examining its unique chemical makeup and the rare environments where it forms through evaporation and alteration.
Mineral Identification and Appearance
Howlite is classified as a borosilicate hydroxide. In its natural state, the mineral is typically an opaque, chalky white or grayish-white color with a sub-vitreous, or slightly glassy, luster. Its most distinctive feature is the erratic, web-like pattern of fine gray, black, or dark brown veins that run through the mass, which are often composed of the surrounding matrix rock. The mineral is relatively soft, registering only about 3.5 on the Mohs scale of hardness, which is comparable to calcite. This low hardness and its porous texture are important characteristics, as they allow the material to be easily carved and also readily accept dye. Natural howlite typically forms in irregular, rounded masses or nodules, which are often described as visually resembling a cauliflower. True crystalline forms of howlite are exceedingly rare and typically only reach a maximum size of about one centimeter.
Unique Geological Formation
Howlite forms primarily within evaporite deposits. The formation process requires a significant source of boron, calcium, and silica, which often become concentrated in these closed basins. These conditions are frequently met in desert climates, where ancient lakes or playas have dried up over long periods. A crucial part of the formation involves the interaction of water with volcanic ash, which provides the necessary silica for the borosilicate structure. As boron-rich water moves through the evaporite sediments, the dissolved elements chemically react and precipitate out, forming the howlite nodules. The mineral often occurs in association with other evaporite minerals, such as gypsum and various borate minerals like borax and ulexite.
Primary Global Deposit Sites
The most significant commercial deposits of howlite are found in North America, particularly in the arid regions of the southwestern United States. California and Nevada are the main sources, where the mineral is typically discovered in association with large borax deposits. The Kramer Borate Deposits and the area around Boron, California, which hosts the world’s largest borax mine, are known for producing large quantities of white howlite. The Tick Canyon area in Los Angeles County, California, is a historically important locality, having yielded large nodules of howlite. Nevada’s arid deserts also contain substantial borax deposits, and mines in areas like Blue Mountain have been noted for producing high-quality specimens. The presence of howlite in these locations is directly tied to the geologic history of extensive Miocene-Pliocene-era evaporite basins in the region. Howlite was first discovered and named in 1868 near Windsor, Nova Scotia, Canada. This initial discovery site, located in evaporite deposits within a gypsum quarry, remains historically relevant, though it is not a primary source for the majority of the material on the commercial market today. Other notable sources of borate minerals, and consequently howlite, include Mexico, Germany, Turkey, and Russia, which contribute to the global supply.