Chalcedony
Mineral NameChalcedony
Chemical FormulaSiO2
Mohs Hardness6.5
Crystal Systemtrigonal
Lusterwaxy
Streak Colorwhite
Cleavagenone
Fractureconchoidal
Specific Gravity2.6
Colorswhite, grey, brown, reddish-brown, blue, orange
Transparencytranslucent
Type LocalityWidespread globally, notable occurrences in Brazil, Uruguay, India, USA
Mineral GroupSilicates
Usesjewelry, ornamental objects, carving material
Associated Mineralsquartz, calcite, zeolites
Raritycommon
Description
This image shows a polished specimen of banded chalcedony, commonly known as agate, displaying concentric layers of white, grey, reddish-brown, and brown with a waxy luster and botryoidal habit.
Geological Context
Chalcedony forms from low-temperature aqueous solutions, often filling cavities in volcanic rocks (like basalt) or as a precipitate in sedimentary environments, crystallizing as microscopic fibers of quartz.
