Datolite is a calcium boron hydroxide nesosilicate, chemical formula CaBSiO4. Crystal system is monoclinic and one variety forms clear prismatic crystals that range from lustrous and sparkly to more frosted, as seen in this specimen from Lane's mine in Westfield, USA. Actual width is 105 mm. Another variety of datolite occurs in botryoidal or nodular masses that are a dull black on the outside and clearly-white microcrystalline inside.