mineral

Bicolor Quartz (Milk Quartz with Slag or Dark Inclusions)

Silicon Dioxide (SiO2) with impurities

Hardness: 7 (Mohs scale); Color: Opaque white (milky) and charcoal grey/black; Luster: Vitreous to waxy; Structure: Hexagonal (trigonal); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Opaque white (milky) and charcoal grey/black
Luster: Vitreous to waxy

Identified March 20, 2026More mineral →

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Physical properties

Hardness: 7 (Mohs scale); Color: Opaque white (milky) and charcoal grey/black; Luster: Vitreous to waxy; Structure: Hexagonal (trigonal); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Milk quartz forms during the late stages of hydrothermal or pegmatitic cooling where trapped gas and liquid bubbles create an opaque white appearance. The dark portion may be caused by inclusions of minerals like tourmaline or graphite, or it could be a contact boundary with host rock or industrial slag if found in post-industrial areas.

Uses & applications

Common quartz is used widely in construction (sand), as an abrasive, in glass manufacturing, and in electronics; bicolored specimens are often kept by local collectors or used in craft lapidary work.

Geological facts

Quartz is the second most abundant mineral in Earth's continental crust. Specimens that exhibit sharp color zoning are often called 'tuxedo stones' by hobbyist beachcombers and rockhounds.

Field identification & locations

Identify in the field by its inability to be scratched by a steel knife (H=7) and its lack of cleavage. This specific water-worn specimen is most likely found in riverbeds or coastal areas where erosion has rounded its edges.

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