Chalcedony
Weight
5-10g
You will be picked one at random
Chalcedony is a cryptocrystalline form of silica, meaning it consists of fine intergrowths of quartz and morganite, which are to small to be seen without a high magnification.
The Crystal system is trigonal due to its primary quartz composition or monoclinic due to its morganite component.
It belongs to the silicates mineral class and its hardness 6.5-7 on the MOHs scale.
Chalcedony is generally a secondary mineral, forming in low temperatures and pressures typically at or near the earths surface.
It is found as nodules, conceptions or layers in limestone and marks as well as cementing agents in sandstone.
It precipitates from low temperature hydrothermal solutions. Chalcedony frequently replaces organic material e.g petrified wood,fossils or other minerals.