Sodalite

Sodalite is a tectosilicate mineral, Na8(Al6Si6O24)Cl2, whose royal blue kinds are widely used as ornamental gemstones; Wikipedia says massive pieces are opaque while crystals are usually transparent to translucent. Cunningham describes a deep blue stone veined with white, often mistaken for lapis lazuli but lacking its golden flecks, and gives Venus and Water. Hall lists blue, mottled dark and light with white, often tumbled, from North America, France, Brazil, Greenland, Russia, Myanmar and Romania. Cunningham uses it for healing of stress-related troubles, to dispel fear and guilt, to still the mind and for wisdom. Hall associates it with joining logic and intuition, deeper meditation, a drive for truth, harmony and trust in groups, release of old mental conditioning, and calm. Her claims about metabolism, radiation and blood pressure are her own and are not vouched for here. Cunningham's table lists lapis lazuli as a substitute.