536 



MINERALOGY. 



Slaty Pot- 



ItHS-ClS}'. 



POTTERS-CLAY. Topferthon, Werner. 

 a. EARTHY POTTERS-CLAY, Jameson Erdiger 

 Topferthon, Werner. 



There are two kinds of this clay, viz. Earthy and 

 Slaty. 



External Characters. Colours white and grey ; 

 very seldom mountain-green. Occurs massive; fri- 

 able, approaching to solid. Internally dull, or feebly 

 glimmering, from intermixed scales of mica. Fracture 

 in the large coarse-grained uneven ; in the small fine 

 earthy. More or less shining in the streak. Frag- 

 ments very blunt-edged. Opaque. Soils slightly. 

 Very soft, passing into friable. Sectile. Adheres 

 strongly to the tongue ; more strongly than loam. 

 Feels rather greasy. Becomes plastic in water. 

 Chemical Characters. It is infusible. 

 Constituent Parts. Silica, . . 6l 

 Alumina. . . 27 

 Oxide of Iron, 1 



Water, . . 11100 

 Klaprolh, Chem. Abhandl. s. 282. 

 Geognos/ic Situation. It is a frequent mineral in al- 

 luvial districts, where it sometimes occurs in beds of 

 considerable thickness; it has also been observed in se- 

 condary or floetz formations. 



Geographic Situation. It occurs in many districts 

 in England, Scotland, and Ireland. 



tTjftv. It is used in potteries, in the manufacture of 

 the different kinds of earthen-ware ; it is also made 

 into bricks, tiles, crucibles, and tobacco-pipes ; and is 

 employed in improving sandy and calcareous soils. 



(b.) SLATY POTTERS-CLAY, Jameson. Schiefriger 

 Topferthon, Werner. 



External Characters. Most frequent colour dark 

 smoke-grey, seldomer bluish and pearl-grey. Occurs 

 massive. Lustre of the principal fracture glistening 

 cross fracture dull. Principal fracture very imperfect 

 slaty; cross fracture fine earthy. Fragments often 

 tabular. Does not adhere so strongly to the tongue as 

 the earthy kind, but becomes more shining in the 

 streak ; feels more greasy. 



Geognoslic Situation. It occurs in considerable beds 

 in alluvial districts, along with earthy Potters-clay. 

 Variegated 3. V ARiEo. ^TEDCLAY, Jameson. BunterThon, Werner. 

 Uav. External Characters. Colours white, grey, yel- 



low, red and brown. Occurs massive. Internally 

 dulL Fracture coarse earthy, inclining to slaty. 

 Fragments blunt-edged. Becomes strongly resinous 

 in the streak, more so than the preceding kinds. 

 Soft, inclining to friable. Sectile. Adheres pretty 

 strongly to the tongue. Feels rather greasy. 



Geognoslic and Geographic Situations. It occurs in 

 alluvial deposites near Wehrau, in Upper Lusatia. 

 Slate-Clay. 4 . SLATE-CLAY, Jameson. Schiefer Thon, Werner. 

 External Characters. Colours smoke and ash-grey, 

 greyish-black, and sometimes bluish and yellowish- 

 grey, and brownish-red. Occasionally contains im- 

 pressions of unknown ferns and reeds. Massive. Dull, 

 or glimmering, owing to intermixed scales of mica. 

 Fracture in the large more or less perfect slaty; in the 

 small, earthy. Fragments tabular. Opaque. Inter- 

 mediate between soft and very soft. Affords a dull 

 grey-coloured streak. Easily* frangible. Adheres 

 slightly to the tongue. Feels somewhat greasy. Spe- 

 cific gravity, 2.636, Karstcn. 2.680, Kirtvan. 



Geognostic Situation. It occurs in beds in all the 

 secondary coal-formations. It passes into claystone, 

 sandstone, and bituminous.shale, and sometimes in- 

 clines to clay-slate. 



Biiumi. 



Claystoue 



Geographic Situation.' It occurs more or less abun- Oryctogr 

 dantly in all the coal-districts in this island. *)' 



5. BITUMINOUS SHALE, Jamesoi,. Brandschiefer, 

 Werner. 



External Characters. Colour light brownish-black, 

 which sometimes passes into blackish-brown. Occurs 

 only massive. Internally lustre feebly glimmering. 

 Fracture rather thin and straight slaty. Fragments 

 tabular. Opaque. Becomes resinous in the streak, 

 but the colour not changed. Very soft, approaching 

 to soft. Rather sectile, and easily frangible. Feels 

 rather greasy. Specific gravity, 1-991, 2.049, Kirivan 

 2.060, Kartlen. 



Geognoslic Situation. - It occurs principally in 

 rocks of the coal-formation, where it frequently al- 

 ternates with, and passes into, slate-clay, and also 

 into coal. 



Geographic Situation It occurs in all the coal dis- 

 tricts in this island, and also in those of Bohemia, Po- 

 land, Silesia, and other countries. 



6'. CLAYSTONE, Jameson. Thonstein, Werner. 

 External Characters. Colours grey, white, blue, and 

 red. Sometimes veined, spotted, and striped. Occurs 

 massive. Internally dull, when it does not contain acci- 

 dentally mixed glimmering particles. Fracture fine 

 earthy, but sometimes passes to fine-grained uneven, 

 and even inclines to slaty and conchoidal. Opaque. 

 Semi-hard, sometimes soft, and even very soft. Spe- 

 cific gravity 2.210, Karsten. 



Geognostic Situation. It occurs in beds, along with 

 porphyry ; also forming the basis of clay-porphyry, 

 in beds, along with black coal, and as a constituent 

 of some kinds of tuff. 



Geographic Situation. It occurs along with second- 

 ary porphyry in the Pentland Hills ; in a similar situa- 

 tion in the island of Arran ; on the mountain of Tinto ; 

 in the Ochil Hills ; and in many other places of Scot- 

 land. 



Uses. When of sufficient hardness, it is used as a 

 building-stone ; also for lintels and door-posts, and can 

 be formed into water-troughs. It forms an indifferent 

 paving-stone. 



7- ADHESIVE SLATE, Jameson. Klebschiefer, Werner. Adhesive 

 External Characters. - Colours grey and white. Slate. 

 Massive. Dull. Fracture straight slaty ; thick or thin 

 slaty. Fragments tabular. Soft, passing into very 

 soft. Sectile. Feels somewhat greasy. Adheres 

 strongly to the tongue. Specific gravity 2.0SO, Klaprolh. 

 Chemical Character. Infusible before the blow- 



Silica, 



Alumina, 



Magnesia, 



Lime, 



Iron and Manganese, 



Water, 



pipe. 



Conslit. Parts. Silica, . . 58.0 



5.0 

 6.5 

 1.5 

 9-0 

 19-9100. 



Buchoh. 



Geognoslic Situation. It occurs in beds in secondary 

 gypsum, and contains imbedded menilite. 



Geographic Situation. It has hitherto been found 

 only in the gypsum formation around Paris. 



8. POLIER, or POLISHING SLATE, Jameson. Poliers- 

 chiefer, Werner. 



External Characters. Colours white, grey, brown, 

 and yellow. Occurs massive. Dull. Principal frac- 

 ture straight and thin slaty; cross fracture fine 

 earthy. Opaque. Soils slightly. Very soft, passing 

 into friable. Uncommonly easily frangible. Feels fine, 

 but meagre. Specific gravity 0.5900.606, Haberle. 



slate. 



