igneous
Graphic Granite
Graphic Granite (variety of Pegmatite)
Hardness: 6-6.5 (Mohs scale); Color: Pink to cream host (K-feldspar) with grey to black quartz inclusions; Luster: Vitreous to pearly; Crystal structure: Intergrown monoclinic and trigonal; Cleavage: Perfect in two directions for feldspar.
- Hardness
- 6-6
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-6.5 (Mohs scale); Color: Pink to cream host (K-feldspar) with grey to black quartz inclusions; Luster: Vitreous to pearly; Crystal structure: Intergrown monoclinic and trigonal; Cleavage: Perfect in two directions for feldspar.
Formation & geological history
Formed from the slow cooling of silica-rich magma in pegmatites. The quartz and feldspar crystallize simultaneously to create a unique interpenetrating texture. Most deposits are Precambrian or Paleozoic.
Uses & applications
Used primarily as decorative stone, in lapidary work for cabochons and spheres, and as a collector's specimen. High-quality pieces are used in jewelry.
Geological facts
The name comes from the Greek word 'grapho' (to write) because the quartz patterns resemble ancient cuneiform or hieroglyphic writing. It is a classic textbook example of simultaneous crystallization.
Field identification & locations
Identify in the field by the 'writing' pattern of darker quartz embedded in a lighter feldspar matrix. Commonly found in pegmatite districts such as those in Maine, California, and South Dakota in the USA.
