Wiktionary
cyanotrichite
n. (context mineral English) A rare, blue, orthorhombic copper aluminium sulfate mineral.
Wikipedia
Cyanotrichite
Cyanotrichite is a hydrous copper aluminium sulfate mineral with formula CuAl[(OH)|SO]·2HO, also known as lettsomite. Cyanotrichite forms velvety radial acicular crystal aggregates of extremely fine fibers. It crystallizes in the orthorhombic system and forms translucent bright blue acicular crystal clusters or drusey coatings. The Mohs hardness is 2 and the specific gravity ranges from 2.74 to 2.95. Refractive indices are nα=1.588 nβ=1.617 nγ=1.655.