HOWLITE on DOLOMITE

Howlite, a mineral composed of calcium borosilicate hydroxide (Ca2B5SiO9(OH)5), is classified as a borate and is typically found in evaporite deposits. 

The mineral was first identified in 1868 by Canadian chemist and geologist Henry How near Windsor, Nova Scotia. Miners in a gypsum quarry initially regarded it as a nuisance, prompting How to investigate further. He initially named it silico-boro-calcite, but it was later renamed howlite by American geologist James Dwight Dana. 

Geologically, howlite is most commonly found in irregular nodules that can resemble cauliflower. While crystals of howlite are rare, they have been discovered in a few locations, including Tick Canyon in California and Iona in Nova Scotia, with maximum crystal sizes reaching about one centimeter. The nodules are typically white, featuring fine grey or black veins in a chaotic, web-like pattern, and exhibit an opaque quality with a sub-vitreous luster. In contrast, the crystals from Iona can be colorless, white, or brown, often displaying translucence or transparency. Howlite has a monoclinic structure, a Mohs hardness of 3.5, and lacks regular cleavage, with prismatic crystals that are flattened on the {100} plane. Crystals from Tick Canyon are elongated along the 010 axis, while those from Iona extend along the 001 axis.