Howlite

Howlite is a calcium borosilicate hydroxide, a borate mineral formed in evaporite deposits. Wikipedia says it was discovered in 1868 near Windsor, Nova Scotia, by Henry How and named by Dana, and that it occurs as white nodules with grey or black veins. Because it is porous it takes dye easily and is often dyed to imitate turquoise. Hall describes marbled stones, often tumbled, in green, white or blue and often artificially coloured. Hall calls it extremely calming and an antidote to insomnia, and associates it with patience, calm and reasoned communication, a still mind, good sleep and meditation, memory and a desire for knowledge. These are Hall's claims, not established fact.