Spinthere

This is an ambiguous mineral; the form of the crystals is more symmetrical than is usual in Axinite, and they are softer and have less lustre than the common kinds: these circumstances may naturally be caused by an admixture of Lime as well as Clorite in them. Haüy and Lucas appear to be uncertain whether Spinthere be only a variety of Axinite, while Bournon and other eminent Mineralogists are decidedly of opinion that it is nothing else. It is found in small very oblique rhomboidal prisms, the three obtuse edges of which are commonly displaced by dissimilar narrow faces. The terminal planes are commonly so large that the crystals look like very obtuse rhombs ; but sometimes they are so small, that the crystals are rather tall prisms, the acute edges of which being truncated, they become six-sided: this happens in minute crystals that are often grooped together. The scintillating appearance observed by Haüy is produced by a number of minute facets parallel to the faces g g in his fig. 240, pl. 86, which are the same as two of the smaller faces upon my figure.

The Spinthere rests upon primitive crystals of Carbonate of Lime, which are covered with a crust of Chlorite that also penetrates those of the Spinthere; it is accompanied by cubes of Iron Pyrites. It has only been found at Maromme, in the department of the Isère in Dauphiny.