Pearl Spar

Having so distinguished an appearance from other carbonates of lime, this has obtained the name of pearl spark, a name it naturally suggests, and by which it is in general easily recognized. We find however, like other subjects in nature, it has its gradations, and consequently blends itself with substances to which at first it seems very little allied. It may be readily traced, as formed from the primitive crystal of carbonate of lime, to an iron ore, consisting for the greater part of oxide of iron, and manganese. The progress, if I may so call it, appears curiously and distinctly marked by the manner of the crystals, which are in the forms of the primitive rhombs, and are white: sometimes however it approaches the appearance of ivory; and as its substance becomes pearly, the nuclei seem to be separating and curving form about the angle of 30° to about 20°; see the figures. They mostly appear of the natural pearly ustre, but are often at length more curled and darkened, and thence may be called spathose iron ores: perhaps they may be called iron ores whenever the common browner aspect seems to indicate as much. Those, however, which have the forms and fracture of crystallized carbonate of lime may be placed as such while they retain the whitish pearly lustre.

Thus different analyses, showing a difference in the proportion of the substances of which it is composed, decide it to be more or less an iron ore.