Chrysocolla

Chrysocolla

Chrysocolla is a hydrated copper phyllosilicate mineral which can occur in the oxidation zone of copper ore deposits. The small pieces shown here were collected from the floor of an adit in the Hafod feddgar mine in central Wales. Dr. Stephen Plant of the Russell society is shown inspecting the deposit which has accumulated on walls and floor in the hundred years or so since the mines closure. Care was taken not to touch the main deposits in the mine.

Quartz

Quartz

Quartz, SiO2  Druzy variety. The term druzy  describes coatings of fine, or small mineral crystals on a base rock, and can be applied to crystals of all minerals. This 22Kg. specimen was collected on the shore line of the Nant y moch reservoir in West Wales, immediately adjacent to the Bryn y rafr mine. The crystals cover about 60%  of the host rock, and are mostly white, but with some iron staining.  

Opal

Opal

Opal,  SiO2 . nH2O  is a hydrated amorphous form of silica, with a water content between 6% and 10%.  Opal is non-crystalline, so it is classed as a mineraloid. Conditions during deposit can determine the gem quality of Opal, for instance, if there is undisturbed deposition of identical sized minute spheres of silica, gem quality Opal is formed.  There is only a hint of "pinfire opal" in the green area of the specimen which was collected in Andamooka, Australia, by the club co-founder, Jim Nicholls.    

Blue john

Blue john

Blue john is a variety of Fluorite, CaF2 Calcium fluoride. The type locality for this mineral is Castleton in Derbyshire, and this specimen came from Treak Cliff cavern in Castleton. Although Blue john is mostly  associated with Castleton, and is sometimes referred to as Derbyshire spar, similar deposits have been discovered in China.

Grossular ( garnet )

Grossular ( garnet )

Grossular,  Ca3Al2(SiO4)3   is a calcium-aluminium species of the garnet group. The colour of Grossular is very variable, dark green, pink, brown, even colourless, and it's crystal classification is cubic, although most crystals are hexoctahedral.  The specimen is from Grova in Southern Norway, an area known for Copper mining. The crystals are cubic, and a very dark brown. They have slightly bevelled edges, and there is a quartz infilling of a fracture which runs through some of the crystals.