Hydrargillite Enlarge
British Mineralogy
Argilla hydrata


  • Class 2. Earths.
  • Order 2. Homogeneous.
  • Gen. 1. Argilla.
  • Spec. Hydrata.
  • Div. 2. Imitative.

Dr. Turton some time ago gave me a specimen from the Barnstaple Quarry, that had rough balls which were much relieved and of peculiar specific lightness; externally resembling Rotten-stone, but harsher, though easily rubbed off, and soiling the fingers. The upper specimens here figured were from Miss Hill, and are not compressed, as is most usual, but nearly spherical and almost detached, having formed in a hollow in the Schist; and it may be possible that the decomposing specimen figured on the left hand has rested in such a cavity, being a flattish congeries of spheres, rather more solid on the under side. The four middle ones were wholly detached. These all show the Blown Oxide of Iron about them.

The lower left hand figure has some segments that have become nearly opaque and whitish, scarcely showing the radii, but. retaining something of the concentric stains in a circular manner, which are not so distinct when the fresh lustre is remaining. They lie in a very irregular mass, probably of the same substance as the rock, but in such a state of decomposition as somewhat to resemble the running cinder of volcanic Basalt or Trap.

Miss Hill also sent me some Spiculæ on small and thin schistose fragments, that were gathered from a soft common clay-like Shale. They are dull, and easily spoiled by touching: in some the fibres are arranged in all directions, as if separated by decomposition and fallen into irregular masses.

The Schist Rock in which these are found is, I presume, nearly the same us the Irish, a dark flinty Schist (Kiesel schieffer of some), and is remarkable for dividing neatly, not only into broad laminæ, but often into columnar pieces mostly rhomboidal, partly resembling some Coal. The Hydrargillite filling the external parts appears to be liable to decomposition.—I understand there is good Slate quarried at the place.

I should not forget to mention a muss of fragments of the rock, lying extremely irregularly, with crystallized but rusty Hydrargillite about the size of a pen, scattered among and holding them together, which I received with these.

Close-up of poster Get a poster »