160
THE GEOLOGIST.
into optical properties ; physical properties ; otlier characters, such as streak, taste, odour, etc ; characters dependent on cohesion ; chemical characters; all of v^hich. are briefly but intelligibly explained. The system of classification adopted is tbat used by Mr. Warington Smyth in his lectures at the School of Mines, and the division is primarily into Non- metallic and Metallic minerals. The former into the five classes of— 1. Carbon and Boron ; 2. Sulphur and Selenium ; 3. Haloids and Salts ; 4. Earths; 5. Silicates and Aluminates. The latter into four classes — 1. Brittle and difficult of Fusibility ; 2. Brittle, easily Fusible and Volatile ; 3. Malleable, not reducible by heat alone ; 4. Noble Metals, reducible by heat alone. This is followed by a list of symbols and signs, and explana- tions of the technical terms used by jewellers and lapidaries. The book consists of 420 closely-printed pages, and is teeming with outline illustra- tions, small, hut carefully executed. As a sample of its plan a single extract will suffice, and at the same time will probably convey information to some of our readers : —
"Chloeite, Werner. Hexagonal ; occurs in tabular six-sided prisms. Colour various shades of dill emerald-green in the direction of the axis, and yeUowis h o hyacinth-red at right angles to it ; also piire white or yellowish. Massive varieties oHve-green. Semi-transparent to sub-translucent. Lustre pearly ; yields to the nail, and when in powder is unctuous to the touch. Streak corresponding to the colour. H. 1 to 1-5. S. G-. 27 to 2-85. Compact chlorite is amor^jhous. Chlorite- slate posseses a slaty structiu'e, and frequently contains imbedded octahedral crystals of magnetic iron, hornblende, and garnets. Earthy chlorite is composed of small pearly, glimmering, scaly particles. It has a somewhat greasy feel, and bears a striking resemblance to Green Earth.
Composition. 4 (Mg Fe), 'a1, Fe, 2 Si, 3 H = 4 Mg Si -h 3 H.
Analysis, from the Pyrenees by Delesse, Silica 32 '1, Alumina 18-5, Magnesia 36-7, Protoxide of Iron O'G, Water 12-1 = 100-0.
Chlorite fi-equently contains as much as 8 or 9 per cent, of protoxide of iron ; those kinds which have more (up to 28 or 29 per cent.) are classed with Eipidohte. Before the blowpipe some lose their colour and fuse at the edges ; with borax aifords an iron-i*eaction. — Localities. The tin mines of Cornwall, where it is well known by the name of peach. Also in Cumbei'land and Westmoreland, and near Llanberis m Caemarvonshne. At Portsoy, in Banflfsliire, it is mixed ^vith Ser- pentine, and is frequently cut and polished. — Name. From ;^Xcop6y, green. This mineral may be distinguished from mica by its laminae being flexible but not elastic, while those of mica are very elastic. It has been proposed by Descloiseaux to divide chloi'ite into tlu*ee groups, Pennine, Clinochlore, and Ripidolite ; to which may be added Leuchtenbergite. — Specimens. British Museum ; Case 52. Museum of Practical Geology ; Horse-shoe Case, ios. 1039—1043, 1047."
In this little book also the various names used by different authors have been introduced, as well as certain terms which, although now obsolete, are very useful for reading the works of the older mineralogists, in which they constantly occur ; while the copious lists of synonyms are very valu- able to the student in perusing the works of foreign authors. We could say much more of its merits. It is very easy to " cut up " a bad book, but it is by no means so easy to say properly all we would of a good one. We can recommend Mr. Bristow's book to our student-readers; and, as its price and dimensions bring it within the reach of every one's means, we advise them to test the value of our praise by buying it and reading it.
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