Click on photo for larger image. Featured specimens diopside granitic type pegmatite diorite granite dolomite marble schist Visitors may touch all rocks and minerals featured on this page. Not all minerals are crystals Made of silica and water, opal has nearly the same chemical composition as quartz yet occurs as a formless mass from a solution of silica in water. Opal remains light and porous and never forms distinct crystals. Few collectible crystals grow from vapor Some elements and compounds dissolve in heated gasses including water vapor.
Vaporized minerals condense when they meet cooler surroundings.