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.

Quartz, Amethyst var.

Quartz, Amethyst var.

Quartz, silicon dioxide, SiO2 has many varieties, dependent on conditions in which it is formed, or the inclusions of trace minerals. Amethyst quartz gains it's purple colour from irradiation, or trace amounts of iron, or both. This specimen from south Australia has a distinctive boundary between two episodes of growth.  The first episode has deposited quartz with just a hint of purple, and the second episode a growth of which is deep purple. This cut and polished slab reveals the outline of the tops of crystals from the first deposition. The inset picture shows the reverse of the specimen.