Hematite

Hematite

Hematite, Fe2O3  is Iron oxide, and the main ore of iron. The location of this specimen is Ton Mawr quarry, Taffs Well, South Wales. The Ironstone deposits are within the Carboniferous limestone of the area, and the iron content is probably derived from the nearby red keuper marls. The specimen shows the characteristic red colour, which gave rise to the name Hematite, derived from the Greek word for blood, haima. There are also vhugs of minute botryoidal Goethite  in the specimen, which was collected by Gwyn Billington, an old friend, and well respected member of the Russell society, in April 1993.

Gypsum

Gypsum

Gypsum is an evaporite mineral with the formula  CaSO4 . 2H2O , Calcium sulphate dihydrate.  This specimen was collected from the beach cliffs at Blue anchor bay, Watchet, in west Somerset. The cliffs are triassic in age, and are alternating layers of green marl and red keuper marl. There are many veins of Gypsum running through the cliffs, and this specimen was collected from a vein in the red marl. The top and bottom of the specimen are fairly solid, and in between weathering has taken place revealing the original growth of Gypsum as it was evaporated from saline water.

Opal

Opal

Opal,  SiO2 . nH2O  is not a mineral, because it has a water content, and so it is classed as a mineraloid, It is classed as a hydrated amorphous form of silica, with a water content usually in the range of  6% to 10%, but it may have as much as 20%. Opal is composed of microscopic spheres of silicon dioxide molecules, which are deposited in closely packed planes. If the planes are very precise and regular. precious Opal is produced, however, most of the time slight discrepancies in how the spheres are deposited, result in "rough Opal". This specimen is rough opal from Madagascar , with just a hint of regular deposition.

Okenite

Okenite

Okenite,  CaSi2O . 5 . 2H2O ( simplistic formula )  is a silicate mineral often found together with zeolites  in basalt geodes. The origin of this specimen is unknown, but it is probably from Poona in India. The "cotton ball" effect is created by thousands of fine fibrous crystals radiating from a central point. The individual crystals, although fragile, have a degree of flexibility. The very pale green colour of the mineral surrounding the Okenite, suggests that it is probably another silicate mineral, Prehnite.

Sphalerite

Sphalerite

Sphalerite, (Zn, Fe)S, sometimes called "Black jack" or "Blende", is Zinc Sulphide, and is the main ore of Zinc. Pure Sphalerite is ZnS, but as it is usually combined with varying amounts of Iron, Fe, the formula is expressed as (Zn, Fe)S.  Sphalerite with very little, or no Iron can be colourless, but as in this specimen, the amount of Iron has produced a dark golden brown colour. There are no complete crystals, only fractured faces, and here and there, just a glimpse of the deep red colour usually associated with Sphalerite, which is a good aid for identification. The white mineral is Calcite, and the specimen was collected from Snailbeach mine, Shelve, Shropshire.