mineral

Rock crystal (clear quartz), possibly cloudy quartz

Quartz, silicon dioxide (SiO₂)

AI-generated identification · may be incorrect

Colorless to milky, transparent, and glassy with internal fractures and inclusions; hardness 7 Mohs, vitreous luster, hexagonal crystal structure, and no true cleavage (conchoidal fracture). The rounded shape suggests a broken or water-worn crystal rather than a complete crystal point.

Identified August 15, 2026More mineral →

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Physical properties

Formation & geological history

Forms in silica-rich hydrothermal veins, pegmatites, and cavities in igneous or metamorphic rocks. Quartz is geologically widespread and may range from Precambrian to recent. The Minas Gerais region near 20.1°S, 42.0°W is well known for quartz-bearing pegmatites and hydrothermal mineralization.

Uses & applications

Used for glass, electronics, abrasives, optical instruments, and countertop materials; clear attractive pieces are sold as display specimens or lapidary rough. This fragment is more likely decorative than gem-grade.

Geological facts

The apparent internal planes are mostly fractures and growth features, not cleavage. Quartz can produce a piezoelectric charge when mechanically stressed.

Field identification & locations

Identify by its hardness, glassy luster, lack of cleavage, and inability to scratch with a steel knife while scratching ordinary glass. A definitive distinction from glass requires testing; bubbles, flow lines, or uniform conchoidal breaks would suggest man-made glass instead.