Tourmaline is a crystalline boron silicate mineral, Na(Li,Al,Mg,Mn,Fe)3Al6(BO3)3 Si6O18(OH)4 This black variety is the most common, over 90%, and is called schorl variety. The crystals are prismatic in the trigonal system, and are intermixed with feldspar. The specimen is from Minas Gerais, Brazil.
Tree agate is a form of chalcedony, which is microcrystalline quartz. SiO2. It's proper name is dendritic quartz, or dendritic agate. The main body is a dirty white with a hint of green. The tree part of the description is an obvious reference to the similarity of the branches of a tree. The green inclusions are dendritic manganese with maybe a small amount of iron. The specimen is from S.W. Australia,and was collected by the club's co-founder, Jim Nicholls, while working in Australia.
Gypsum, CaSO4 . 2H2O Calcium sulfate dihydrate. is an evaporate mineral deposited as salt laden lakes dry up, This variety is known as "satin spar" and is from Spain. It's appearance suggests that it came from a seam enclosed by other rocks.
Agate is a variety of chalcedony, and is a silicon dioxide mineral SiO2 This polished specimen has been named as seam agate. Seam agate as opposed to an agate geode. The lack of colour in the specimen leads to the conclusion that it may be a cold water agate formed under less volatile conditions. Cold water agates are typically colourless or grey, The specimen is translucent allowing some light to pass through a five cm. section. The outer surface is rough and pitted. an imprint of the matrix from which it came. The origin is only known as N.S.W. Australia.
Galcte, calcium carbonate, CaCO3. These spheres of calcite in a basalt cavity, appear to be quite common at the site of Viterbo, Montalo di castro, Central Italy. Each sphere is an agglomerate of thousands of microscopic scalenahedral crystals.