Volltext Seite (XML)
Argillaceous Genus affedU rhomboidal form; fome of thefe inclofe rounded pebbles of the fame fubftance. By ex- polure to the air it acquires an ochry cruft. In- ternally it hath fome luftre from a number of mi- nute fbining particles. Fradture, nearly even, and fine fplintery, yet often inclining to the flat conchoidal. Opake. Hardnefs 9. Sp. er. 2748 bymytrial. & * n .* Heated in an open fire it becomes magnetic, and lofes about 3 per ct. ofits weight lt does not i.edden ; but at 98° melts into a lomevvhat po- rous black xnaTs, partly porcelain, and partly an enamel. According to the analyfis of Dr. Withcring, it contains 0,475 file x, 0,325 argill, 0,20 calx of iron. Here we may obferve, ift, thatit contains nocalx; that it contains lefs iron than araijl; and, 3d, that the iron is in acalqiform ftute. In thefe refpedts then it differs from many traps, and from baialts; hence I call it fentöle. iVhin-fione is a name ufed in England, Scot land, and the North of Ireland. It is of a blue, or greyifh black colour, whofe hardnefs is~from 8 to 9. Sp. gr. from 2,4 to 2,hü, is often a tiap. It is found in detached fragments, or for- ming dykes in mines; ol thefe a curious account by Mr. Mills, may be feen in the J'hil. Tranf* for 1790, p. 73, The bafis of the cellular ftoijc, calied amyo-- daloid, the mandelfteinof the Germans, is alfo frequently a rrap, gcnerally of a greyifh, black- ifh or reddifh brown, or yellovvifh black, orgrecn- ifh grey; and has its holes fillcd vvith quartz, fpar, or calcedony, often with bole, &c. or empty; and the fides of an cchry, or bluifh grey colour, deriyed