Ichthyophthalmite Enlarge
Dec 1 1811 published by Jas Sowerby London.
Exotic Mineralogy
XXVI
Silex Ichthyophthalmus

Ichthyophthalmite

  • Syn.
    • Apophyllite. Haüy Tabl. 36, Journal des Mines, 137. 388.
    • Fischaugenstein. Werner.
    • Ichthyophthalm. Karsten.

Found at Ute, or Uton, in Sweden, It has been placed in the Feldspar family, but as the analysis does not detect any Alumine, it cannot belong to the Clay or Feldspar genus, which ahvays contains some, and mostly from twenty to thirty per cent. It is a rare mineral, and its pearly lustre is compared to that of a fishes eye, whence its name. The crystals are commonly rectangular, or nearly rectangular tables, variously lengthened and truncated. It is about as hard as common glass, with considerable lustre, and pearly on the larger faces. The fracture is parallel with the planes of the table, and mostly splendid; the cross fracture is somewhat shattery and glistening. It varies in colour, but is generally white, or very pale red, blue, green, &c. Spec. Gray. 2.491, Froths and melts by means of the blow-pipe into an opaque bead.

Our upper figure is taken from a specimen in the collection at the British Museum. The numerous, somewhat reddish tabular crystals, intersecting each other in various directions, rarely have their edges defined; they seem to be part of a vein enclosed betwixt some decomposed Honblend. The loft hand crystal below is from a valuable specimen in the extraordinary fine collection of crystals of the Count de Bournon, by whose friendship it is here figured. It exhibits modifications upon the vertical edges, which are very rare. The right hand figure exposes some neat crystals with truncations upon the angles; it is in the possession of Mr. Lowry.

Blend and Galæna sometimes accompany this mineral.

The Count de Bournon considers the so called variety of Stilbiie from Strontian (B. M. tab. 258) as a variety of Ichthyophthalmite; this point requires elucidation.

Analysis of Ichthyophthalmite.
By Fourcroy and Vauquelin. By Rose.
Silex 51 55    
Lime 28 25    
Potash 4 2.25
Water 17 15    
Loss 0 2.75
100 100
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