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Sponges (Porifera) are a group of simple animals. They possess a porous ' spongy' texture and no definite external organs or form. They vary in shape and hardness. The sponge body consists of a mass of cells of various kinds forming a delicate tissue, and this is supported on a skeleton of minute rods, or spicules, of calcite, silica or of a horny organic substance.
 Research Sponge
A Nicol prism is a device composed of two prisms of Iceland spar or calcite cut at specified angles and cemented together with Canada balsam. It is used for producing plane-polarized light.
Research Nicol Prism
In minerals, an allomorph is any one of two or more distinct crystalline forms of the same substance; or the substance having such forms, for example carbonate of lime occurs in the allomorphs calcite and aragonite. The term
allomorph describes a variety of pseudomorph which has undergone a partial or complete change or substitution of material. Thus limonite is frequently an allomorph after pyrite.
Research Allomorph
Amygdaloidal is a name given to igneous rocks, usually old lava flows, full of almond-shaped cavities which have been filled up with secondary minerals, such as calcite, agate or the zeolites. These cavities vary in size up to several centimetres across and were formed while the rock was still fluid and in motion.
Research Amygdaloidal
Analcime is a mineral of the zeolite group noted for its vitreous lustre, and has the formulae NaAlSi2O6ù2H2O and a relative hardness of 6. It is found in the cavities of intrusive and volcanic igneous rocks; often as clear shiny crystals and is associated with calcite and other zeolites. Analcime was first identified on islands off Sicily and was confirmed as a distinct mineral in 1797 by the French mineralogist Rene-Just Hauy.
Research Analcime
Apophyllite (so called from its foliated structure or easy cleavage), also called fish-eye stone is a hydrothermal mineral filling cavities in basalt and tufaceous rocks. It is associated with stilbite, scolecite, calcite, prehnite, analcime. It has the formulae KCa4Si8O2O(OH)ù8H2O and a relative hardness of 5.
Research Apophyllite
Aragonite (named from Aragon in Spain) is a mineral identical in composition with calcite or carbonate of lime, but differing from it in its crystalline form and some of its physical characters. It forms easily in a sedimentary environment but only stable in metamorphic rocks formed at high temperatures. It has the formulae CaCO3 and a relative hardness of 4.
Research Aragonite
Argentine is a siliceous variety of calcite, or carbonate of lime containing a little silica, having a silvery-white, pearly lustre, and a waving or curved lamellar structure. It is found in primitive rocks and frequently in metallic veins.
Research Argentine
Azurite is a minor ore of copper with an intense azure-blue colour. It alters to malachite and is associated with limonite, calcite, chalcocite, chrysocolla and other secondary copper minerals.
Azurite reacts vigorously with hydrochloric acid. It has the formulae Cu3(CO3) 2(OH)2 and a relative hardness of 4.
Research Azurite
Baryto-calcite is a mineral of a white or grey colour, occurring massive or crystallized. It is a compound of the carbonates of barium and calcium.
Research Baryto-Calcite
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The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
©1993 - 2009 The Probert Encyclopaedia
Southampton, United Kingdom
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