Agate
Quartz var. Agate · Semi-Precious Gemstone and Mineral Specimen
Crystal System
Trigonal, microcrystalline (Chalcedony) forming in massive, nodular, or banded habits
Mineral Group
Silicates, specifically Tectosilicates
Chemical Formula
SiO2
Formation Process
Hydrothermal and secondary sedimentary deposition, where silica-rich groundwater fills cavities in volcanic rocks in rhythmic, successive layers over long periods
About This Crystal
A small, tumbled pebble displaying distinct concentric banding in shades of brown, white, and translucent grey. It has a waxy to vitreous luster, smooth tumbled texture, and exhibits the classic microcrystalline banded structure characteristic of agate
Physical Characteristics
Colors range from earthy browns and whites to translucent greys, white streak, no cleavage, conchoidal fracture, specific gravity around 2.60 to 2.65, brittle tenacity, and occasionally faint fluorescence under shortwave UV
Optical Properties
Uniaxial positive, doubly refractive with a refractive index of approximately 1.544 to 1.553, typically translucent to opaque with aggregate birefringence
Hardness & Durability
Origin Region
Found worldwide including Brazil, USA (Lake Superior region), India, Madagascar, and Germany, typically in volcanic cavities and ancient lava flows
Hardness & Durability
Mohs hardness of 6.5 to 7, good toughness due to microcrystalline interlocking structure, very durable and highly suitable for jewelry and tumbling
Care & Maintenance
Easy to care for; can be cleaned safely with warm soapy water and a soft brush, store away from direct sunlight and harder minerals to prevent scratching
Rarity & Value
Common and widely available, value depends heavily on unique banding patterns, color vibrancy, size, and fine polish, with most tumbled pieces being very affordable
Special Characteristics
Distinct concentric color banding, microcrystalline structure, and the ability to take a high polish which enhances its natural patterns
Lore & History
Historically used by ancient civilizations like the Egyptians and Greeks for amulets, seals, and ornamentation. In modern crystal lore, agate is traditionally associated with grounding, emotional balance, stability, and protection