Galena, Eyam.

Galena, Eyam.

Galena, lead sulfide, PbS   The irregular boundary of the galena is probably because  it is composed of rather large integrown cubic crystals. On either side of the galena there is fluorite. For the main the fluorite is in massive form, but with a few small crystals exposed just under the galena. There is a second, smaller layer of galena lower down, with small pieces of galena embedded in the massive fluorite. less obvious from the front view, but very obvious from the side. The specimen is from the Ladywash mine in Eyam, Derbyshire.  

Antigorite, serpentine var.

Antigorite, serpentine var.

This specimen, known as "precious serpentine" is a sub-species of antigorite, which in turn is one of several minerals in the serpentine family. In common with all polymorphs of serpentine it has the formula of (Mg,Fe)3Si2O5(OH)4) Precious serpentine is so named because it can be fashioned into jewellery or carved ornaments. It was collected by Jim Nicholls, co-founder of the club, from Sailors Gulley, Mt.Crawford, in south Australia, while working there.

Picrolite, serpentine var.

Picrolite, serpentine var.

Picrolite is a sepentine mineral. It is a variety of antigorite, which is a polymorph of serpentine. There are two other important polymorphs of serpentine, chrysolite, and lizardite.  Serpentine, antigorite, chrysolite, lizardite, and picrolite are all hydrous magnesium iron phyllosilicate,  and have the same formula,  (Mg,Fe)3Si2O5(OH)4).  Each polymorph has a different habit, which in the case of picrolite is platey, bordering on fibrous. It's origin is Estrie, Vancouver.

Aragonite.

Aragonite.

Aragonite is calcium carbonate, Ca CO3. It has the same formula as calcite and vaterite, but has a different crystal lattice. Repeated twinning of the crystals produce the pseudo hexagonal  crystals as in this specimen . The whole of the surface of this ball is covered with crystals, some with a brown colouration,  with no sight of the base rock. The specimen is from an aragonite outcrop in Tazouta, south of Sefrou, Morocco, and is one of many similar specimens from this site.

Astrophyllite.

Astrophyllite.

Astrophyllite is a rare mineral. It is hydrous potassium iron silicate with the formula  ( K,Na )3(Fe++,Mn)7Ti2Si8O24(O,OH)7 It's name is derived from two Greek words, astron meaning star, and phyllon meaning leaf, and these descriptions are easily observed in the specimen. The crystals are described as bladed  with a sub metallic shine dependant on the viewing angle. The whole of the specimen is a radiating, stellate, aggregate, with glimpses of the sub metallic shine, within a light coloured felsic matrix. Unfortunately it's origin is unknown.