Carbonate of Lime in lenticular rounding crystals has long since been shown in tabs. 62 and 63, and the many varieties otherwise rounding, either crystallized as those of tabs. 418, 419, and 420, or in rounded grains, or globose, but not apparently depending upon the laws of crystallization, as in tabs. 8, 38, and 384. The present variety, consisting of granules formed by an assemblage of crystals, seems to be peculiar to the Coal formation, and remarkable for having long escaped the notice of mineralogists. I have it as small nearly as Ketton-stone, in Coal from South Wales; and when the mass contains a hollow, as it sometimes does, we see the surface of the grains, and discover them to be little groups of nearly lenticular crystals, more or less mingled with Oxide of Iron, and almost every side covered with the Coal, or seemingly cemented by it: they are rather ovate than rounded (otherwise they would compare with Sulphate of Binies, tab. 96); but sometimes compress each other a little, forming flatfish faces where they meet, often having a brassy iridescence, giving them a metallic appearance, It is rather curious that they should form a stratum in the midst of a thick stratum of Coal in the neighbourhood of Dudley in Staffordshire, where they are called Brazils or Brasses by the miners. They lay in a nearly regular series, of three or four inches in thickness. I have a specimen four feet long and two feet wide, with these regularly passing from one end to the other. The miners consider their presence as a sign of good Coal. They bring blocks up from the pits to make posts with, and find them very durable. Pyrites is sometimes near them: but the specimen I have, which had been out of the ground some years seems not likely to decay. It should seem from the lower figure of tab. 105, that in certain cases the Sulphuret of Iron keeps together, and in others it effloresces, and is used in the manufacture of common vitriol.
Coals have most of the varieties of Sulphuret of Iron, l>otli of crystallization and durability. Mr. Farey seems to understand the durable sort to be the Brazils, and the other the Brasses of some of the miners. See Farey’s Derbyshire Index, &c.—I do not know of these but as miners’ terms.
This sort of Oolithus (or Pea-stone as some would call it,) demanded illustration somewhere, and may lead to some useful theory.