Page:Transactions NZ Institute Volume 15.djvu/494
Opal, S̈i, Ḣ, or S̈i Ḣ3.—The more valuable varieties are not known in New Zealand, but the inferior qualities are of common occurrence.
Hyalite is mentioned by Dr. v. Haast as occurring in small masses, lining cavities in the volcanic rocks of Snowy Peak and the Malvern Hills (Jurors' Rep. N.Z. Ex., 1865, p, 256), and again in a few localities in the volcanic rocks of Banks Peninsula (Trans. N.Z. Inst., vol. xi., p. 511), and is also mentioned by Professor Liversidge (Trans. N.Z. Inst., vol. x., p. 496) lining cavities in the vesicular grey trachytes of Bell Hill, Dunedin.
Common Opal and Semi-opal are mentioned by Dr. v. Haast (Jurors' Rep. N.Z. Ex., 1865, p. 256) as filling small cavities in the quartz porphyries of the Malvern Hills and Mt. Somers, and last year I obtained from the drift of Owharoa a specimen which is of a pure milky-white colour.
Wood Opal (Silicified Wood) is very common where siliceous rocks are decomposing as at Petrifying Gully, Mount Somers. It is mentioned by Dr. v. Hochstetter (New Zealand 1863, Eng. ed., p. 96) in the tuffs and conglomerates of Coromandel, and by Dr. Haast (Juror's Rep. N.Z. Ex., 1865, p. 256) from many localities in Canterbury.
Pitch Opal.—A specimen from Dunstan is described by Prof. Liversidge (Trans. N.Z. Inst., vol. x., p. 496) as follows:—"Brown, variegated, light and dark shades. Hardness about 6. When heated in closed tube gives off water, blackens, and emits empyreumatic odour; the condensed water has an acid reaction, and on evaporation leaves a carbonaceous residue which blackens on ignition; breaks with a well-marked conchoidal fracture; contains iron." There are two specimens of this mineral in the collection of the Colonial Museum—one from the Harper Hills, and the other from the Rakaia Gorge.
Opal-jasper.—There is in the collection of the Colonial Museum a specimen of opaline quartz with jasper, from the trachyte tufa of Portobello, Otago, which forms a very pretty ornamental stone. The predominating colours as described by Prof. Liversidge (Trans. N.Z. Inst., vol. x., p. 496) are red-brown, blue-grey, and opal-white.
Siliceous Sinter.—Deposits of this class are found surrounding several of the thermal springs, and have been well described by Dr. v. Hochstetter (New Zealand, 1863, Eng. ed., pp. 398, 412). He says, in speaking of the siliceous deposits of Orakeikorako: "The sediment of this, like all the surrounding streams, is siliceous; the recent sediment is soft as gelatine, gradually hardening into a triturable mass, sandy to the touch, and finally forming, by the layers deposited one above the other, a solid mass of rock of very variable description at different places both as to colour and structure. Here it is a radiated fibrous or stalky mass of light brown colour; there a chalcedony hard as steel, or a grey flint; at other places the deposit