Tanzanite forms as a brownish crystal and is trichroic, which means it shows three colors – brown, blue and violet – concurrently. Heating, either underground naturally by metamorphic processes, or artificially, removes the brown or burgundy color component to produce a stronger violet-blue color and makes the stone "dichroic", which means it only reflects blue and violet. Rarely, gem-quality tanzanite will heat to a green primary hue, almost always accompanied by a blue or violet secondary hue. These green tanzanite have some meaningful value in the collector market, but are seldom of interest to commercial buyers.