Agate (Banded)
Quartz variety Chalcedony (Agate) · Semi-Precious Gemstone / Decorative Stone
Crystal System
Trigonal (Hexagonal) - Microcrystalline; Habit is typically massive, botryoidal, or filling geodes with rhythmic concentric banding.
Mineral Group
Silicates (Tectosilicate)
Chemical Formula
SiO2 (Silicon Dioxide) with trace inclusions of iron, manganese, or aluminum
Formation Process
Hydrothermal; formed by the deposition of silica from groundwater into cavities (vesicles) of volcanic rock or limestone.
About This Crystal
A translucent to opaque microcrystalline quartz featuring distinct curved color banding. Luster is vitreous to waxy. Surface is smooth when tumbled or polished.
Physical Characteristics
Color: Grayish-white with dark gray/blue bands. Streak: White. Cleavage: None. Fracture: Conchoidal. Specific Gravity: 2.60–2.64. Fluorescence: Often inert or faint greenish-white under UV.
Optical Properties
Refractive Index: 1.530–1.540. Birefringence: Up to 0.004. Generally displays no pleochroism. Translucency depends on band thickness.
Hardness & Durability
Origin Region
Brazil, India, Botswana, and Lake Superior (USA); found in volcanic cavities or sedimentary environments.
Hardness & Durability
Mohs Hardness: 6.5–7. Toughness is high (very durable due to fibrous structure). Excellent wearability for jewelry.
Care & Maintenance
Wash with warm soapy water and a soft brush. Safe for ultrasonic cleaners if no fractures present. Generally stable in sunlight.
Rarity & Value
Common; Value is determined by pattern complexity, color contrast, and size. Highly affordable and often dyed to enhance color contrast.
Special Characteristics
Rhythmic banding (fortification banding) caused by varying impurities during the silica layering process. Periodic growth layers.
Lore & History
Used since the Neolithic era for amulets and tools. Historically used in Ancient Egypt for seal stones and beads. Traditionally associated with grounding and stability.