132 EARTHS. ARGILLACEOUS. 39. Opalus. 



with effervefcence, and communicates no colour to it : ef- 

 fervefces (lightly with foda, and melts into a mafs ipotted 

 with red : with microcofmic f^lt, it gives a pearl-colour 

 globule: contains filica 53- alumina 20. potal's 18. fiuat 

 of lime 5, oxyde of manganefe 3. oxyde of iron i. 

 Klaproth^ 



39. OPALUS. Confifting of alumina, the greater 

 proportion of filica, with a little oxyde ol iron, 

 and generally fome carbonate of magnefia and 

 carbonate of lime: hardiHi, fhining, hardly ever 

 opake, of a conchoidal texture, light, breaking 

 into indeterminate fragments, prtrafitica), gene- 

 rally of a common form, cafily cracking into 

 clefts: melting with the greatetl: difficulty. 



^ydrophtt" Somewhat opake, becoming tranfparent and changing its 

 ^h colour in liquids, adhering to the tongue. 



Achates unguium colore. ^)it. nat. xii. 3./. 6g. k, 6. d. 

 Achates, &c. Wall fyst. min^ i. ^. 283. «. 21. 

 Hydrophane. Kirnvan mineral. 1. /». 295. 

 Oculus mundi, H;. drophan. Schmeifser mineral. I. f. 14N 

 Hydrophane, Oculus mundi, Thoinfon chem^ 3* P' S'^'i' 

 Fcund in the Feroe ijlandiy Iceland, Bitanny, Hungary, Si-efia^ 

 and Germany, generally accompanying other It-^ncs of the 

 genus, or in the ftate of incruitation in concad w-.th Opal, 

 Chalceaony, Prafe, Chryfoprafs, Serp;:ntine, Granite, Ne- 

 phrite, Jafper, Porphyry, and indurated Clay: colour white, 

 yellow, red, or green : becomes gradually tranlparent vvhtn 

 foaked in water by imbibing the liquid, and is iometimef, 

 though rarely, found in the form of a 3-lided pyramid; 

 contains filica 93. alumina i or 2. water, inlldininitDle mat- 

 ter and air 5, with iometimes a l.'tile iron, 



piceus* Of a waxy luftre, and imperfe£lly conchoidal textuje, 



Pitchllone. Kir<wun \. p. 292, Schmeifser minsr. \. p. 145, 

 Pitchftone. Thom/on chem. 3. /. 529, 



Found in amorphous mafTes of v^anous lize, in France, Germany^ 

 Saxony, and various parts ot Europe, and in Ntoi' Spain : co- 

 lour greyifh-black, greenifn-brown, blueifh j^rcy, leek or 

 olive-green, red or yel'iowilh, tranfparent, lenutranipdrent or 

 opake, frequently piefenting large or fmail j^rainea diltinfl 

 concretions: luilre a little greafy: fpeciii': gr^vi-.y r .n 

 2,314. to 2,645. certains fi'^ica 7 3,co, alumina i4,t:o, lime 

 1,00, oxyde of iron 1,00. oxyde of aian^iUKii o,iO, foaa 

 if7S' '^'^ater 8,50. Klaproth* 



