Gypsum

Gypsum

Gypsum,  CaSO4 . 2H2O  Calcium Sulphate dihydrate, is an evaporite mineral. This specimen was formed as a saline residue arising from the evaporation of an enclosed basin of sea water. Of the two specimens, one appears to be a loose aggregate, and the smaller one has obvious layering. The location is loosely given as Crete.

Analcime

Analcime

Analcime, Na(AlSi2O6) . H20  is a tectosilicate and classed as a zeolite. The specimen is from Croft quarry in Leicestershire, which is a noted site for Analcime. The quarry is in Igneous tonalite rocks of Ordovician age. The few crystals on the base of the specimen are trapezohedral in form.

Manganese oxide.

Manganese oxide.

Manganese Oxide,  MnO2,  dendritic variety. The specimen was collected from the abandoned Llanymynech limesone quarry about 20 years ago. Sometimes the Manganese oxide is wrongly referred to as Pyrolusite,  but there are several Manganese oxides, and only laboratory analysis can determine which of the  oxides is present. Dendritic Pyrolusite is rare, and more often than not, it is one of the other oxides. Trace elements of other minerals will determine which one.

Hematite

Hematite

Hematite Nodule,  Fe2O3  Iron oxide. with Siderite and Quartz.  This specimen was found on my final visit to Marine colliery waste heaps. Hoping to find some Millerite, I arrived to find that the waste heaps had been landscaped out of existence. As I was despondently leaving the remaining tiny car park, I spotted this nodule by the entrance, which did at least give me something to show for my 136 mile round trip. The centre of the nodule is lined with tiny platey Siderite crystals, with two small crystals of Quartz.

Jasper

Jasper

Jasper,  Mookaite var.  SiO2 , is not a mineral as such, but is a rock. It is formed as a sedimentary rock from the weathered products of a cretacious siltstone in the Carnarvon basin in Western Australia. In particular it derives it's name from Mooka station, where it was first found. Jasper is an aggregate of microgranular quartz, and chalcedony. The specimens reddish colour is the result of iron impurities, and the typical conchoidal fracture of quartz is apparent. This specimen was collected by Jim Nicholls, co-founder of the club, while he was working in the area.