igneous
Quartz-rich pegmatite with purple amethyst
Granite pegmatite; crystalline quartz (SiO₂), locally amethyst (purple quartz)
AI-generated identification · may be incorrectCoarse, irregular interlocking quartz crystals in a pale feldspar-rich matrix, with lilac-purple coloration from amethyst; quartz hardness 7, vitreous luster, no cleavage, hexagonal crystal structure, specific gravity about 2.65. Feldspar is softer (Mohs 6) and commonly shows cleavage.
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Physical properties
Coarse, irregular interlocking quartz crystals in a pale feldspar-rich matrix, with lilac-purple coloration from amethyst; quartz hardness 7, vitreous luster, no cleavage, hexagonal crystal structure, specific gravity about 2.65. Feldspar is softer (Mohs 6) and commonly shows cleavage.
Formation & geological history
Likely a late-stage igneous pegmatite formed when silica-rich magma cooled slowly in a vein or cavity, allowing unusually large crystals; commonly Paleozoic to Precambrian in age depending on locality.
Uses & applications
Attractive pieces are used as mineral specimens, lapidary material, and occasionally ornamental stone; amethyst portions may be cut for jewelry, though this specimen appears matrix-rich and mainly collectible.
Geological facts
Purple color results from trace iron and natural irradiation in quartz. The tan and pink matrix likely contains feldspar with weathered iron-bearing minerals.
Field identification & locations
Identify by very hard, glassy quartz that scratches ordinary glass, pale cleavable feldspar, and coarse pegmatitic texture; common in granitic terrains worldwide, including Brazil, Uruguay, Madagascar, and the United States.
