Agate (Commonly known as Chalcedony/Banded Agate)
Quartz var. Agate · Semi-Precious Gemstone / Decorative Stone
Crystal System
Trigonal/Hexagonal system in a microcrystalline (cryptocrystalline) fibrous habit. Typically occurs as nodular, botryoidal, or massive layers within geodes.
Mineral Group
Silicates (Subgroup: Tectosilicates)
Chemical Formula
SiO2 (Silicon Dioxide) with micro-inclusions of iron oxides (Fe2O3) or manganese and aluminum trace elements
Formation Process
Hydrothermal / Sedimentary; formed by the deposition of silica from groundwater into cavities in igneous rocks or as replacement of organic material.
About This Crystal
Exhibits a waxy to vitreous luster with translucent to opaque sections. Notable for its microcrystalline structure which often creates concentric or planar banding. The image shows a smooth, polished surface with diffused earthy tones and pale, milky white patches.
Physical Characteristics
Color: Variable (white, brown, grey, cream); Streak: White; Cleavage: None; Fracture: Conchoidal to uneven; Specific Gravity: 2.58–2.64; Fluorescence: Variable, sometimes glows green or yellow under UV light.
Optical Properties
Refractive Index: 1.530–1.543; Birefringence: Up to 0.009; No pleochroism; Aggregates are typically doubly refractive but difficult to measure due to microcrystalline nature.
Hardness & Durability
Origin Region
Brazil, Uruguay, India, Madagascar, and USA (notably Lake Superior and Oregon). Found typically in volcanic cavities and sedimentary rock pockets.
Hardness & Durability
Mohs Hardness: 6.5–7; Toughness: Very high due to interlocking micro-fibrous structure; Highly durable for all types of jewelry.
Care & Maintenance
Clean with warm soapy water and a soft brush; avoid ultrasonic cleaners if the stone is dyed. Generally stable but can be sensitive to hydrofluoric acid; stores well away from harder stones like sapphire.
Rarity & Value
Common; Value is driven by banding patterns, color intensity, and size. Generally inexpensive except for rare varieties like Fire Agate or Iris Agate. Often subjected to dyeing to enhance color.
Special Characteristics
Banded structure, translucency, and potential for 'moss' or 'dendritic' inclusions. Some specimens show a 'fortification' pattern resembling a castle map.
Lore & History
Historically used in ancient Sumeria and Egypt for amulets and cylinder seals. Traditionally associated with grounding, protection, and stabilizing energy in various cultures. Associated with the Root or Sacral chakras depending on color.