mineral
Milky Quartz Pebble with Hag Stone Feature
Crystalline Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Opaque white (milky); Luster: Vitreous to greasy; Crystal Structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Opaque white (milky)
- Luster
- Vitreous to greasy
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Physical properties
Hardness: 7 on Mohs scale; Color: Opaque white (milky); Luster: Vitreous to greasy; Crystal Structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed from hydrothermal solutions or cooling magma rich in silica. The milky appearance is caused by tiny fluid inclusions of gas or liquid trapped during crystal growth. This specific shape is the result of water erosion in a high-energy environment like a river or beach.
Uses & applications
Used in construction aggregates, glass making, abrasives, and as decorative garden stones or lucky charms (hag stones).
Geological facts
The hole in the center, which makes this a 'hag stone' or 'adder stone,' is usually formed by the boring action of specialized organisms like piddock clams or by localized erosion of a softer inclusion. In folklore, such stones were believed to protect against witchcraft and evil spirits.
Field identification & locations
Identified by its waxy-to-glassy luster, extreme hardness (it will scratch glass), and opaque white color. They are ubiquitous in riverbeds and along coastlines globally.
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