The brownish material is chlorargyrite, AgCl, also sometimes called cerargyrite or horn silver. Chlorargyrite is often white, yellow or light brown when fresh, — Photo: Nessa Eull · CC0
Chlorargyrite
Also known as: Horn silver.
Natural silver chloride — a secondary mineral of oxidized silver deposits, and historically a valuable 'horn silver' ore.
Intro adapted from Wikipedia (CC BY-SA).
Chlorargyrite is an IMA-recognized mineral species in the halide class, with the chemical formula AgCl.
It crystallizes in the cubic crystal system (space group Fm3m).
Key properties: Mohs hardness 2.5; specific gravity 5.556; typically white or gray or colorless or purple; White streak; Resinous to adamantine, waxy luster; refractive index 2.071; optically isotropic.
IMA symbol Cag, IMA status: approved, named in 1565.
May be a rich ore in the oxidized zone above silver deposits; commonly preserved in arid climates.
It is found associated with Silver, cerussite, iodargyrite, atacamite, malachite, jarosite, Fe–Mn oxides.
The name refers to CHLORine, and the Greek for silver, argyros, in its composition.
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