Native arsenic is usually found as granular or curvilaminar masses, with a reniform or botryoidal surface.
It is never crystallized, but may have a fibrous or microcrystalline structure, and commonly occurs in concretionary forms or in compact and earthy masses; sometimes mammillated, botryoidal, reniform or stalactitic. The colour presents various shades of brown and yellow, and the streak is always brownish, a character which distinguishes it from haematite with a red, or from magnetite with a black streak.
This genus, from the Permo-Carboniferous of Autun, is represented by large, fleshy, reniform leaves or leaflets, with radiating dichotomous venation; the vascular bundles have in all respects the structure of those in the leaves of Cycads or Cordaiteae.
A compact variety of a pale liver-brown colour and forming concentric layers with a reniform surface is known in Germany as Schalen- blende or Leberblende.
The reniform masses are known as kidney ore.
However different in structure Trilobites may be, they all agree in possessing a head-shield usually semi-circular in shape, which results from the fusion of apparently five segments, and bears, except in some blind forms, a pair of large reniform compound eyes like those of the king-crab (Xiphosura).
Some peaches have globular, others reniform glands, others none at all, and these latter trees are much more subject to mildew than are those provided with glands.