Agate
Quartz var. Agate (Microcrystalline Chalcedony) · Semi-Precious Gemstone / Decorative Stone
Crystal System
Trigonal/Hexagonal system; typically forms in microcrystalline/cryptocrystalline massive or nodular habits
Mineral Group
Silicates (Tectosilicate)
Chemical Formula
SiO2 (Silicon Dioxide) with inclusions of iron and manganese oxides
Formation Process
Sedimentary/Hydrothermal: Forms as a secondary mineral in volcanic rock cavities (vesicles) or sedimentary layers via silica-rich groundwater
About This Crystal
A translucent to opaque tumbled stone with a waxy to vitreous luster. It exhibits a mottled brown, tan, and earthy red color palette with characteristic banding and moss-like inclusions.
Physical Characteristics
Color: Multicolored (brown/tan); Streak: White; Cleavage: None; Fracture: Conchoidal; Specific Gravity: 2.58-2.64; Fluorescence: Often inert or weak yellow-green
Optical Properties
Refractive Index: 1.530-1.540; Birefringence: Up to 0.004; Optical Character: Uniaxial positive; typically shows no pleochroism
Hardness & Durability
Origin Region
Globally found; notably Brazil, Uruguay, India, and the United States (Lake Superior region)
Hardness & Durability
Mohs Hardness: 6.5 to 7; High toughness due to microcrystalline structure; excellent stability and wearability
Care & Maintenance
Clean with warm soapy water and a soft brush. Avoid harsh chemicals and sudden temperature changes, though generally very durable.
Rarity & Value
Common; value is determined by pattern uniqueness, size, and color vibrancy. Generally affordable and widely available.
Special Characteristics
Displays banding, mottling, and translucency; some specimens may show dendritic or moss-like inclusions of iron/manganese.
Lore & History
Historically used for amulets and hardstone carving in Ancient Greece and Egypt. Traditionally associated with grounding, emotional balance, and physical protection.