Clinoclase with Quartz (#77)
|North America||Tin Stope, Majuba Hill, Pershing Couty, Nevada||2" x 1 ½" x 1 ¼"|
Clinoclase is Cu3(AsO4)(OH)3, and the crystal structure looks like this (black=arsenic, blue=copper, red=oxygen, pink=hydroxyl, which is OH):
The black box is the unit cell. Clinoclase has one direction of perfect cleavage and is quite soft. Is it clear to you from the structure drawing why this is so?
Clinoclase is built in layers, and the layers are "attached" to one another only by weak hydrogen bonds. Hydrogen bonds can be represented as O-H···O, where the three dots symbolize a weak electrostatic attraction between the positive H atom bonded to its oxygen and another nearby oxygen to which it is not chemically bonded. The occurs across the gap between layers, as the hydrogen of a pink OH group is attracted to a negative oxygen atom (red) in the next layer. So when clinoclase is scratched or cleaved, only the weak H···O "bonds" are broken.