mineral

Agate (Grey Agate Slice)

Microcrystalline Quartz (SiO2)

Hardness: 6.5–7 on Mohs scale; Color: Grey, black, and cloudy white bands; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.58–2.64.

Hardness: 6
Color: Grey, black, and cloudy white bands
Luster: Waxy to vitreous

Identified April 6, 2026More mineral →

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Physical properties

Hardness: 6.5–7 on Mohs scale; Color: Grey, black, and cloudy white bands; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.58–2.64.

Formation & geological history

Formed as a secondary mineral in volcanic rock cavities (vesicles) or sedimentary formations. Silica-rich groundwater percolates through cavities, depositing layers of chalcedony over thousands of years. Ages can range from millions to hundreds of millions of years.

Uses & applications

Used in gemstone jewelry (pendants, beads), ornamental items (coasters, bookends), and industrial applications like leather-burnishing tools and mortar/pestles due to its high hardness.

Geological facts

Agate is a variety of chalcedony characterized by its banding. Grey agate is often considered a stone of 'grounding' in metaphysical circles. Some grey agates are dyed to produce more vibrant colors like blue or pink.

Field identification & locations

Identify by its translucent nature when held to light, waxy luster on broken surfaces, and distinct concentric or parallel banding. Commonly found in Brazil, India, and the United States (specifically Lake Superior and Oregon).

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