Howlite is a calcium-containing borosilicate, which is most commonly used to simulate a variety of more valuable ornamental materials. Occurring as cauliflower-like microcrystalline masses, the mineral is very suitable for this purpose as its whitish coloration and high level of porosity allows for the easy and effective absorption of dyes. In addition, because some specimens also possesses dark veining, dyed howlite can be especially convincing when used as an inexpensive turquoise simulant. However, it should be noted that these two materials are completely unrelated to each other, so the term “white turquoise” is a misnomer.

The mineral was first discovered in 1868 by the Canadian geologist Henry How in his native Nova Scotia, but California is the primary source of howlite today. These are also the only two localities in the world that produce the rare colorless macrocrystals, which can grow up to one centimeter in length.