An introduction to the study of minerals : with a guide to the mineral gallery / by L. Fletcher.

  • British Museum (Natural History). Department of Mineralogy
Date:
1914
Catalogue details

Licence: In copyright

Credit: An introduction to the study of minerals : with a guide to the mineral gallery / by L. Fletcher. Source: Wellcome Collection.

    20/128 (page 18)
    The study of the present configuration of the Earth’s crust is accordingly left to the Geographer, and the historical aspect of the materials to the Geologist; the Mineralogist deals, not with the Earth’s configuration past or present, but with the characters, localities of occurrence, changes and associations of the matter itself, and deduces principles on which to classify the various kinds. Soil. 4. The first mineral product met with in the examination Specimen, of the solid portion of the Earth is usually a loose Soil, which on inspection is found to be a mixture of fragments of substances of different kinds, and to be such as would result from the wearing away of the more compact matter in the neighbourhood. Rock. 5. Beneath the loose soil is a firmer material, retaining Specimen much the same character generally over a considerable area of °chist.a country and sometimes for a considerable depth ; to such a material the term liocit is applied. Rocks are As in soil, so also in most kinds of rock the unaided eye Specimen, generally jg ap]e detect different kinds of matter*. composite. . ... . The illustrative specimen in the case is a fragment ot a rock called Granite; mere inspection teaches us that in this specimen at least three different kinds of matter come together—first, a substance of alight brown colour, with some of its surfaces quite smooth and plane (Felspar); secondly, a substance of a glassy aspect, milky colour and irregular shape (Quartz) ; and, thirdly, a dark-coloured substance apparently made up of thin leaves (Mica). By a process of mechanical division we can thus extract from this fragment of rock at least three kinds of substances; and these will prove to be distinct from each other, not only in outward appearance, but in all their manifold properties. Simple 6. It will be found, however, that by no amount of mechanical Specimens, minerals, (Jivisi0n can any of these three substances be made to yield another having a different set of characters; they are Simple Minerals. Other 7. The compositeness of some rocks is less evident to Specimen rocks' the naked eye, and requires the aid of a microscope for ofdiabase- its demonstration.