I

610 MARCASITA.

whole ftrata , though sometimes in detach'd masses ; very freely and readily giving fire withfees not fermenting with j acid menflruums , inflammable , yielding a blue sulphureousflame , and afterwards calcining into a purple powder .

i. Marcajita ar gent ea.

Silver colour d Marcafite .

' HIS is a very elegant and beautiful body, of a very firm and compact, thoughsomewhat irregular texture 5 and very remarkably heavy. It is naturally foundconstituting whole strata of very great extent, though never of any great thickness,from three inches to a foot in depth being their usual standard: but sometimes likemany other bodies naturally consisting strata, it is found in large irregular and brokenmasses. It is, when broken, of a very irregular and uneven surface, and is seen to bemade up of multitudes of irregularly fhap’d flaky bodies, of very various sizes, and notdifpos’d with the least regularity, but oddly contorted, and wav’d, and wraping roundone another. In some masses of this body this structure is seen very distinctly, the se-veral plated bodies being mote loosely conjoin’d; but in others it is scarce distinguish-able to the naked eye, the whole being as it were run into one solid mass, and thecomposition more close : and such is the variety of this body, that this difference isoften perceived in the space of an inch of the fame fragment of the body. Its colouris an extreamly bright white, very much like that of silver, but much more gaudyand glittering.

It very freely and readily gives fire with steel.

It makes no effervescence with Aqua Fortis.

When put into the fire it cracks and bursts, yielding a blue flame with a sulphureoussmell: it burns thus for a considerable time, and finally calcines to a strong deep red.

The Microscope shews its structure to be the fame in its most solid parts as it is seenby the naked eye in the more lax ones.

This is the usual appearance of this body, but it is liable to a vast number of varie-ties ; sometimes it contains a large quantity of lead ore, sometimes of that of tin, andvery often a dusky brown ferrugineous matter is intimately mix’d with it; at other timessome of the cubic or regularly figur’d Phlogoniæ are immers’d in it; and sometimes,where it has room, its constituent flakes rife on its surface in conjunct series, and forma very elegant foliaceous top to it. Nor is this all, for very frequently where there hasnot been enough of it to form a stratum, it has been deposited in small specks of a moreor less complex, but always flaky structure on Stones or ores of various kinds, and thususually makes a very beautiful and glittering appearance frequently, beside its naturalbright white shining with all the colours of the rainbow on different parts of its surface,as they are differently turifd to the light.

It is found in vast abundance in the lead and tin mines of all parts of England, andis no less common in other countries; our counties of Devonshire, Derbyshire, andCornwal, abound with prodigious quantities of it.

2. Marcajita aurea.

Gold colour d Marcajite.

This is a more beautiful and glittering species than the former. It is of a moderatelyfirm structure, but less compact texture than any other Marcasite. It is considerablyheavy, and is usually found in long but very thin strata, sometimes accidentally in largeand mis-shapen nodules. It breaks with a moderate blow, and is seen to be compos’d of avery irregular congeries of flat flaky Moleculæ, resembling multitudes of irregular frag-ments of leaf gold, crouded confusedly into a compact mass. In some parts of this spe-cies the texture is, as in the other Marcasites, more lax and open than in others; but itis every where plainly distinguishable; and it is indeed to this irregularly foliaceousstructure of the Marcasites that all their other varieties are originally owing. It is na-turally of a fine strong gold yellow, but varies at times into a paler or more intense hue,and like the others sometimes gives the several rainbow colours in reflection. It is al-ways very bright, but not at all transparent.

It gives fire pretty readily with steel, but much less freely than the former species.

It