mineral

Milky quartz with iron-oxide staining

Quartz (SiO₂), likely massive vein quartz

AI-generated identification · may be incorrect

White to gray, translucent patches with a glassy-to-dull luster and irregular fracture; hardness about 7 Mohs, no cleavage, specific gravity ~2.65. Dark specks and yellow-brown areas are likely iron/manganese oxides or minor inclusions, while the granular areas may include feldspar or weathered host rock.

Identified September 7, 2026More mineral →

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Physical properties

Formation & geological history

Formed when silica-rich hydrothermal fluids filled fractures, later crystallizing as quartz veins; staining developed during weathering. Precise age cannot be determined from the photograph. Quartz veins are common in the Precambrian and younger crystalline rocks around southeastern Brazil.

Uses & applications

Common quartz has low commercial value as a rough specimen, though it is used for glass, ceramics, abrasives, and engineered stone; clear attractive pieces may be used decoratively.

Geological facts

Quartz is one of Earth’s most abundant minerals and lacks cleavage, producing curved or uneven fracture surfaces. It can scratch ordinary steel or glass, though this test may damage the specimen.

Field identification & locations

The rounded, weathered white mass and hard glassy grains fit vein quartz; test with a steel file or glass, and inspect for a consistent quartz vein texture. The reported Rio de Janeiro-region location is geologically plausible for quartz-bearing crystalline rocks.