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MINERALOGY. 



MINERALOGY. 



850 



bustibles, and metals : Haiiy divided minerals into acidiferous earthy 

 substances, earthy substances, non-metallic combustible bodies, matallic 

 bodies, substances not sufficiently known to admit of classification, 

 rocks, and volcanic products. In Phillips's ' Elements of Mineralogy,' 

 the classes are earthy minerals, alkaline-earthy minerals, acids, acidi- 

 ferous earthy minerals, acidiferous alkaline minerals, native metaU, 

 metalliferous minerals, and combustible minerals. Berzelius attempted 

 a strictly chemical classification of minerals : he has however candidly 

 admitted that considerable difficulties attend this method, owing, in 

 part at least, to the uncertainty which exists as to what are the essen- 

 tial and what the accidental constituents of a mineral. 



The following is the arrangement of Dufrenoy as given in Professor 

 Ansted's ' Elementary Course of Geology,' &c. : 



Class I. Simple Bodies, or Binary Compounds never bases, generally 

 essential ingredients in combinations, and serving as proximate 

 elements. 

 Group 1. Hydrogen. 



2. Carbon. 



3. Silicon. 



4. Sulphur. 



5. Selenium. 



Class II. Alkaline Salts. 

 Group 1. Salts of Ammonia. 



2. Salts of Potash. 



3. Salts of Soda. 



Class III. Alkaline Earths, and Earths. 

 Group 1. Salts of Barytes. 



2. Salts of Strontia. 



3. Salts of Lime. 



4. Salts of Magnesia. 



6. Salts of Yttria. 



6. Salts of Alumina. 



Clasra IV. Silicates. 

 Group 1. Anhydrous Aluminous Sililcates. 



2. Hydrous Aluminous Silicates. 



3. Silicates of Alumina and Lime, or their isomorphs. 



4. Aluminous and Alkaline Silicates, and their isomorphs. 



5. Hydrous Aluminous Silicates with Alkaline and Lime 



bases, and their isomorphs. 



6. Non-aluminous Silicates. 



a. With Lime as a base. 



b. With Zircon as a base. 



c. With several bases. 



7. Silico-Aluminates. 



8. Silico-Fluates. 



9. Silico-Borates. 



10. Silico-Titanates. 



11. Silico-Sulphurets. 



12. Aluminates. 



Class V. Metal?. 

 Group 1. Cerium. 



2. Manganese. 



3. Iron. 



4. Chromium. 



5. Cobalt 



6. Nickel. 



7. Zinc. 



8. Tellurium. 



9. Cadmium. 



10. Antimony. 



11. Arsenic. 



12. Mercury. 



13. Titanium. 



14. Tantalium. 



15. Niobium. 



16. Pelopium. 



17. Ilmenium. 



18. Lead. 



19. Tin. 



20. Bismuth. 



21. Iran him. 



22. Tungsten. 



23. Molybdeum. 



24. Vanadium. 



25. Copper. 



26. Silica. 



27. Gold. 



28. Platinum. 



29. Indium. 



30. Osmium. 



31. Rhodium. 



32. Palladium. 



Dana, in his useful ' Manual of Minernlopy,' adopts the following 

 clanification : 



JCAT. HIST. DIV. VOL. III. 



Class I. Gases ; consisting of or containing Nitrogen or Hydrogen. 



Class II. Water. 



Class III. Carbon, and Compounds of Carbon. 



Class IV. Sulphur. 



Class V. Haloid Minerals : Compounds of the Alkalies and Earths 

 with the Soluble Acids, or of their Metals with Chlorine or 

 Fluorine. 



1. Salts of Ammonia. 



2 .Salts of Potash. 



3. Salts of Soda. 



4. Salts of Barytes. 



5. Salts of Strontia. 



6. Salts of Lime. 



7. Salts of Magnesia. 



8. Salts of Alumina. 



Class VI. Earthy Minerals : Silica and Siliceous or Aluminous 

 Compounds of the Alkalies and Earths. 



1. Silica. 



2. Lime. 



3. Magnesia. 



4. Alumina. 



5. Glucina. 



6. Zirconia, 



7. Thoria. 



Clasa VII. Metals and Metallic Ores. 



1. Metals easily oxidisable : Iron, Lead, Copper, Mercury, 



fa, 



2. Noble Metals : Gold, Silver, Platinum. 



We have already observed that Mineralogy includes a knowledge 

 of the chemical composition and of the external and physical pro- 

 perties of minerals, and they are all divisible into two great classes of 

 crystallised and uncrystallised. With respect to regularly crystallised 

 minerals, we refer for an account of their forms to what is stated 

 under CRYSTALLOGRAPHY. There are some substances which do not 

 assume regular forms, but have an imperfect crystalline structure ; 

 while those bodies which are not either crystallised or crystalline, 

 unless they are pulverulent, are described as massive, and these are 

 subdivided into such as possess particular forms, as botryoidal, mam- 

 mellated, nodular, stalactitic, reniform, globular, and amorphous, or 

 without any particular form. 



The structure of minerals is an important feature. It may be 

 Columnar, Lamellar, or Granular. The following are explanations of 

 the terms used in describing the different kinds of columnar struc- 

 ture : 



Fibrous : when the columns are minute and lie in the same direc- 

 tion, as gypsum and asbestus. Fibrous minerals very commonly have 

 a silky lustre ; a fibrous variety of gypsum, and one of calc-spar have 

 this lustre very strongly, and each is often called satin-spar. 



lleticulated : when the fibres, or columns, cross in various directions, 

 and produce an appearance having some resemblance to a net. 



Stellated : when they radiate from a centre in all directions, and 

 produce a star-like appearance. Stilbite and gypsum are examples. 



Radiated, divergent : when the crystals radiate from a centre 

 without producing stellar forms. Examples, quartz, gray antimony. 



In the Lamellar Structure the lamina; or leaves may be thick, or very 

 thin ; they sometimes separate easily, and sometimes with great diffi- 

 culty. When the lamina; are thin and separate easily, the structure 

 is said to be Foliaceous. Mica is a striking example, and the term 

 Micaceous is often used to describe this structure. When the lamina; 

 are thick, the term Tabular is often applied ; quartz and heavy spar 

 afford examples. The lamina: may be elastic, as in mica, flexible, as 

 in talc, or graphite, or brittle, as in diallage. Small lamina; are some- 

 times arranged in stellar shapes ; this occurs in mica. 



When the grains in the texture of a mineral are coarse, it is said 

 to be Coarsely Granular, as in granular marble ; when fine, Finely 

 Granular, as in granular quartz ; and if no grains can be detected with 

 the eye, the structure is described as Impalpable, as in chalcedony. 

 Granular minerals, when easily crumbled by the fingers, are said to 

 be Friable. 



Massive minerals also take certain imitative shapes, not peculiar to 

 either of these varieties of structure. The following terms are used 

 in describing imitative forms : 



Globular : when the shape is spherical or nearly so : the structure 

 may be Columnar and Radiating, or it may be Concentric, consisting of 

 coats like an onion. When they are attached, they are called Im- 

 planted Globules. 



Reniform : kidney-shaped. In structure, they are like globular 

 shapes. 



Botryoidal : when a surface consists of a group of rounded promi- 

 nences. The prominences or globules usually consist of fibers radiating 

 from the centre. 



Mammillary : resembling the botryoidal, but consisting of larger 

 prominences. 



Filiform : like a thread. 



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