GEOL 3015__Minerals Lab__2016W.pdf

GEOL 3015__Minerals Lab__2016W.pdf - GEOL 3015 Introductory...

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G EOL 3015 : Introductory Geology For Engineers Rock Forming Minerals Laboratory 1: R OCK F ORMING M INERALS INTRODUCTION The Nature of Minerals A mineral is a naturally occurring inorganic substance possessing a more or less definite chemical composition and a particular combination of physical properties by means of which it may be recognized. Let us look at some of the features of this definition. Firstly, a mineral should properly occur in nature and be the result of the operation of natural processes. Artificial minerals do exist, for example, in concrete or baked bricks, but we should term them “artificial” and try not to confuse them with natural substances. Minerals should be inorganic and chemically homogenous. Coal belongs to the so-called “mineral kingdom”, but it is not a mineral in the true sense for it is formed from once-living plant tissue and so is organic and not inorganic in origin. Granite belongs to the mineral kingdom also, but it is not a mineral because it consists of a mixture of minerals whose proportions vary from place to place; granite, in fact, is a rock. We say that a mineral has a “more or less” definite chemical composition. Many minerals have a very exact chemical composition which can be written as a precise and simple chemical formula, but one of the peculiarities of many minerals is that one chemical element can replace another of closely similar atomic size and physical properties without having much effect on the characteristics of the mineral as a whole. This is because the various properties of minerals depend upon the manner in which the elementary particles of matter are arranged inside the mineral itself. Ultimately, minerals are built from simple particles of matter or elements . The smallest fragment of an element that can exist and still retain all the properties of the element is the atom. An atom of gold is quite different from an atom of silver or an atom of oxygen. Some minerals, like diamond, consist of two elements of a single elementary substance (carbon); others, like rock salt or halite, consist of two elements (sodium and chlorine), arranged in a regular alternating pattern; still others, like mica, consist of many elements arranged in complex, but very regular patterns. The chemical properties of the mineral depend mainly upon the kinds and proportions of the elements which are present, but the physical properties depend more upon the way in which the atoms are arranged than upon the chemistry. In order to find out the chemical composition of a mineral we have to carry out a long and complicated qualitative and quantitative analysis, whereas the physical properties can be determined by a relatively small number of simple tests which, though they may not be conclusive, usually enable us to identify the particular mineral species.
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  • Fall '17
  • Dr. Conly
  • Mineralogy, Introductory Geology For Engineers

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