Agate (Druzy Agate)
Quartz (Chalcedony) var. Agate · Semi-Precious Gemstone / Decorative Stone
Crystal System
Trigonal/Hexagonal; microcrystalline (cryptocrystalline). Specimen is a polished crescent moon with a druzy geode center representing a macro-crystalline quartz cavity.
Mineral Group
Silicates (Tectosilicate subgroup; Quartz group)
Chemical Formula
SiO2 (Silicon Dioxide)
Formation Process
Hydrothermal/Sedimentary process where silica-rich groundwater deposits layers of chalcedony inside rock cavities over time, often ending with macro-crystalline druzy quartz in the center.
About This Crystal
A polished, crescent-shaped stone featuring translucent to opaque gray and white banding. It displays a waxy to vitreous luster on the polished surfaces and a crystalline, sugary texture in the central 'druzy' vug where macro-quartz crystals grew.
Physical Characteristics
Color: Banded gray, white, and translucent; Streak: White; Cleavage: None; Fracture: Conchoidal to uneven; Specific Gravity: 2.58–2.64; Fluorescence: Usually inert or faint yellowish-white under longwave UV.
Optical Properties
Refractive Index: 1.530–1.543; Birefringence: Up to 0.004; Pleochroism: None. This specimen is doubly refractive but appears aggregate under a polariscope due to its cryptocrystalline nature.
Hardness & Durability
Origin Region
Brazil, Uruguay, and India are primary sources. Typically forms in gas cavities (vesicles) within volcanic rocks (basalt or rhyolite).
Hardness & Durability
Mohs Hardness: 6.5–7. It is highly durable and stable, though the druzy center is prone to snagging or collecting dust.
Care & Maintenance
Clean with warm soapy water and a soft brush for the druzy area. Generally resistant to light, but avoid harsh chemicals like hydrofluoric acid. Ultrasonic cleaners are safe if there are no significant internal fractures.
Rarity & Value
Common. Value depends on the aesthetic of the banding and the quality of the druzy pocket. Polished shapes like this are affordable decorative items.
Special Characteristics
This specimen features a 'druzy' center—a cluster of tiny quartz crystals that provide a sparkling, sugary effect inside the host agate.
Lore & History
Historically used for hardstone carving and amulets in ancient Egypt and Mesopotamia. In modern crystal healing, it is associated with stability, grounding, and the Third Eye chakra, traditionally believed to harmonize yin and yang.