igneous
Graphic Granite (Zebra Rock)
Pegmatitic Granite (composed of Quartz and K-Feldspar)
Hardness: 6-7 (Mohs scale), Color: Creamy white or salmon pink background with black/gray angular markings, Luster: Vitreous to pearly, Crystal structure: Intergrown angular monoclinic and trigonal crystals, Cleavage: Distinct on feldspar faces, Specific gravity: 2.5-2.7
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Creamy white or salmon pink background with black/gray angular markings, Luster: Vitreous to pearly, Crystal structure: Intergrown angular monoclinic and trigonal crystals, Cleavage: Distinct on feldspar faces, Specific gravity: 2.5-2.7
Formation & geological history
Formed from the simultaneous crystallization of quartz and alkali feldspar from a water-rich magma (pegmatite) during the final stages of cooling. These rocks typically date from the Precambrian to the Mesozoic eras and form in deep-seated plutonic environments.
Uses & applications
Used primarily as decorative stone, architectural veneers, high-end countertops, jewelry cabochons, and as a popular specimen for mineral collectors due to its unique runic appearance.
Geological facts
The name 'graphic' comes from the Greek word 'graphos' (writing) because the angular quartz inclusions resemble ancient cuneiform or Hebrew lettering. It is a classic example of a 'eutectic' texture where two minerals crystallize at the same time and temperature.
Field identification & locations
Identify in the field by the distinct 'hieroglyphic' or 'script' pattern of dark quartz embedded in light feldspar. Often found in pegmatite dikes in regions with exposed basement rock like the Black Hills (SD, USA), Madagascar, and Scandinavia. Collectors should look for high contrast between the two minerals for the best aesthetic value.
