On the mineralogy of the counties of Dublin and Wicklow / by Samuel Haughton.

  • Samuel Haughton
Date:
[1878]
Catalogue details

Licence: Public Domain Mark

Credit: On the mineralogy of the counties of Dublin and Wicklow / by Samuel Haughton. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    4/10 page 2
    3 The Constituent Albite Feldspar has, hitherto, been found in separate crystals, in one locality only (Dalkey); but it enters largely into the composition of the granite rocks. Its chemical composition is as follows : — Albite (Dalkey Quarry.) Silica, Alumina, Potash, Soda, Fluorspar* 4. The Constituent White Mica (Margarodite) of the granites, often occurs in flat rhombic prisms, or in hexagonal plates, formed from the former by the replacement of the acute angles ; the angles of the lozenges are 120° and 60°; and the crystals are Biaxial, the plane of the optic axes tracing the major diameter of the lozenge. The following measurements of the angle between the optic axes have been recorded :— 1. Three Rock Mountain, . . 53° 8' 2. Glendalough, . . . 70 4 3. Mount Leinster, . . . 72 18 4. Lough Dan, . . . 70 0 5. Glenmalure, . . . 67 11 6. Poulmounty, . . . 76 15 The average chemical composition of the white mica is as follows:— Margarodite (Mean of four specimens.) Silica, 44-58 per cent. Alumina, 32-13 >> Iron peroxide, . 4-57 99 Lime, 0-78 77 Magnesia, 0-76 >7 Potash, 10-67 77 Soda, • . 0-95 77 Loss by ignition, 5-34 99 99-78 The amount of water of crystallisation present in this mineral * The Albite was found in small crystals, lining cavities in the granite, and encrusting crystals of Orthoclase ; and it was associated with similar small crystals of accidental purple fluorspar, from which it was separated with difficulty. 64-70 per cent. 21-80 2-84 9-78 0*80 99 99 99 99-92
    digitised image 1
    digitised image 2
    digitised image 3