Andesite is a crystalline igneous rock, occurring mostly in lava flows, but sometimes in dykes and veins. It consists principally of plagioclasefeldspar, and is often porphyritic, showing large crystals of feldspar scattered through a fine-grained mass, usually of small feldspar crystals, but often containing much glassy material. Andesite forms most of the recent volcanic rock of the Andes, and is thus named after the Andes. Research Andesite
Diabase is a dark, intrusive, basic igneous rock made up of plagioclasefeldspar crystals, surrounded by smaller grains of pyroxenes, such as augite and up to ten percent quartz. Diabase is formed from magna that has cooled just below the Earth's surface, and is sometimes found as intrusions in older rock. A common place to find diabase is in the neck of old volcanoes, where it has formed a plug. Research Diabase
Feldspar or felspar is a name given to a group of minerals, closely related in crystalline form, and all silicates of alumina with either potash, soda, lime, or, in one case, baryta. They occur in crystals and crystalline masses, vitreous in lustre, and breaking rather easily in two directions at right angles to each other, or nearly so. The colours are usually white or nearly white, flesh- red, bluish, or greenish. The group includes the monoclinic (orthoclastic) species orthoclase or common potash feldspar, and the rare hyalophane or baryta feldspar; also the triclinic species (called in general plagioclase) microcline, like orthoclase a potash feldspar; anorthite or lime feldspar; albite or soda feldspar; also intermediate between the last two species, labradorite, andesine, oligoclase, containing both lime and soda in varying amounts. The feldspars are essential constituents of nearly all crystalline rocks, as granite, gneiss, mica, slate, most kinds of basalt and trachyte, etc. The decomposition of feldspar has yielded a large part of
the clay of the soil, also the mineral kaolin, an essential material in the making of fine pottery. Common feldspar is itself largely used for the same purpose. Research Feldspar
Gabbros are basic rocks solidified under great pressure at considerable depths in the earth's crust. They are coarse-grained and consist of plagioclasefeldspar with augite. Sometimes the term is used to include similar rocks composed of the same feldspar with other minerals, and according to the minerals contained they are known as norites, troctolites, eucrites, etc. Research Gabbros
Labradorite has the formulae (Na,Ca)AlSi3O8 and a relative hardness of 6. It is one of the plagioclase feldspars, also known as soda-lime feldspars. Others in the grouping are: albite, oligoclase, andesine, bytownite, and anorthite.
Labradorite often has a beautiful display of colours. The name is derived from the locality of Labrador. Research Labradorite
Microcline is a mineral with the formulae KAlSi3O8 and a relative hardness of 7. It has the same composition as orthoclase but is distinguished by triclinic twinning (usually requiring a microscope to detect). If a feldspar is a deep green it is microcline - and sometimes called 'amazon stone' or amazonite after the Amazon river. It is recognisable from plagioclase by a lack of striations. Research Microcline
Abbreviations
Research Andesite
