Agate Nodule
Quartz var. Chalcedony · Mineral Specimen / Semi-Precious Gemstone
Crystal System
Trigonal, Microcrystalline habit forming rounded nodule
Mineral Group
Silicates (Tectosilicate)
Chemical Formula
SiO2
Formation Process
Sedimentary and Hydrothermal deposition in cavities of volcanic rocks
About This Crystal
A weathered, rounded brownish-grey nodule showing rough external cortex, characteristic of chalcedonic agate weathered out from host rock
Physical Characteristics
Color ranges from brown to grey; white streak; no cleavage; conchoidal fracture; specific gravity around 2.60 to 2.65; brittle tenacity
Optical Properties
Sub-translucent to opaque in rough form; microfibrous quartz structure creating aggregate optical properties with no strong pleochroism
Hardness & Durability
Origin Region
Worldwide, commonly found in weathered volcanic and sedimentary deposits
Hardness & Durability
Mohs hardness of 6.5 to 7; good toughness and durability making it suitable for lapidary work
Care & Maintenance
Clean with warm soapy water; avoid harsh acids; store separately from softer minerals to prevent scratching
Rarity & Value
Common; very affordable as raw mineral specimens unless displaying rare banding or color patterns
Special Characteristics
Often contains microcrystalline quartz banding, sometimes hollow with quartz or amethyst crystal linings inside
Lore & History
Historically used as amulets for protection, grounding, and balancing emotional energy in various ancient cultures