igneous
Granite or granitic gneiss boulders
Quartz–feldspar–mica granitoid; possibly banded gneiss
AI-generated identification · may be incorrectTypically coarse-grained, gray, and speckled with quartz, feldspar, and dark mica; Mohs hardness about 6–7, vitreous to dull luster, interlocking crystals, and poor cleavage. The pale diagonal line is likely a quartz vein or healed fracture; the upper rock may show foliation or weathering.
Identified More igneous →
Explore Granite or granitic gneiss boulders in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Typically coarse-grained, gray, and speckled with quartz, feldspar, and dark mica; Mohs hardness about 6–7, vitreous to dull luster, interlocking crystals, and poor cleavage. The pale diagonal line is likely a quartz vein or healed fracture; the upper rock may show foliation or weathering.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep underground, while gneiss forms when granite is regionally metamorphosed under high heat and pressure. Exact age cannot be determined visually; these may be glacially transported landscaping or field boulders.
Uses & applications
Used extensively as crushed aggregate, dimension stone, paving, monuments, countertops, and landscaping rock; attractive specimens have modest decorative or educational value.
Geological facts
Quartz veins commonly fill fractures with silica-rich fluids after the host rock forms. Rounded surfaces and mixed rock types can indicate glacial transport.
Field identification & locations
Identify by visible quartz and feldspar grains, gray color, lack of vesicles, and very high durability; a streak test is ineffective. Common worldwide, especially in continental shields and glaciated regions.
