A Guide to Geology Author:John Phillips Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: PART III. DESCRIPTIVE AND PRACTICAL GEOLOGY. CONSTITUENT INGREDIENTS OF ROCKS. 89. It has already been stated (§ 10.), that notwithstanding the immense... more » variety of rocks which solicit the attention of a geologist, a correct knowledge of only a limited number of mineral substances is sufficient to enable him to trace and recognise these rocks, and describe them satisfactorily to others. The following short list includes those that appear most essential for this purpose. It is hardly necessary to observe that the student will do well to endeavour to familiarize himself with these minerals, by considering the variation of their appearance and modes of combination with one another, and examining them in a crystallized, amorphous, and decomposed state. For this end he should often contemplate arranged cabinets of minerals, and collect fragments of compound rocks. A little practice will give him a knowledge of their characteristic forms, hardness, specific gravity, and ordinary optical characters. 17. Carbonate of mag nesia 18. Sulphate of lime. 19. Muriate of soda. 20. Bitumen. 21. Iron, Oxide of. 22. Sulphuretof. 1. Quartz.9. Schorl.2. Felspar.10. Chiastolite.3. Mica.1 1. Chlorite.4. Hornblende.12. Green earth.5. Actinolite.13. Talc.6. Augite.14. Steatite.7. Hypersthene.15. Garnet.8. Diallage.16. Carbonate of lime.Those geologists who have occasion to examine into the history of mineral veins, must, in addition, make themselves acquainted with metals, alloys of metals, and combinations of metal with sulphur, selenium, carbon, oxygen, and acids. 90. To assist in the acquisition of the requisite knowledge of these minerals, the following statement of some of the modes of their occurrence in a considerable number of rocks may be found useful. (See also...« less