Page:Transactions NZ Institute Volume 15.djvu/484
2. Crystals of Barytes.—Thames. A very interesting specimen, consisting of an encrustation of small white transparent crystals, the largest being about ⅛ inch across. These crystals are all tabular, and consist of the prism ∞P (a), the macropinacoid ∞P∞ (b), the brachypinacoid ∞P̆∞, and the basal pinacoid OP (d), thus forming octagonal plates. In some crystals the macro- and brachypinacoids are developed to the extinction of the planes of the prism, when four-sides tabular plates are formed, and in others again the macrodome ½ P∞ (e) and the brachydome P̆∞ (f) either bevel the edges of the macro- and brachypinacoid or completely extinguish them, giving rise to the following crystals:—
3. Barytes with Quartz.—Opotiki. A massive variety of a yellowish colour cementing irregular pieces of quartz. This specimen was presented to the museum by the late Rev. Richard Taylor.
4. Radiating Barytes.—Waikouaiti. A specimen presented to the museum by the Hon. W. B. D. Mantell, M.L.C.
Witherite, Ḃa C̈.—The occurrence of this mineral in some of the mines at the Thames is mentioned by Mr. Skey (Geol. Rep., 1870–71, p, 85), but we have not, unfortunately, any specimen in the museum collection.
Salts of Lime.
Calcite, Ċa C̈.—This mineral is so widely distributed in New Zealand in various forms that it is unnecessary to refer to every instance of its occurrence which has been mentioned.
Crystallized Calcite.—Dr. Hector mentions its occurrence in the tertiary rocks of Otago (Jurors' Rep. N.Z. Ex., 1865, p. 3), as Dogtooth Spar in limestone at Moeraki, and as Iceland Spar in limestone, marble, etc. (Jurors' Rep. N.Z. Ex., 1865, p. 437); and Dr. v. Haast (Jurors' Rep. N.Z. Ex., 1865, p. 256) mentions it in cavities of the volcanic rocks of Canterbury. Professor Liversidge also (Trans. N.Z. Inst., vol. x., p. 491) mentions 16 different specimens of calcite from Dunedin, which are all crystallized as rhombohedrons or combinations of the rhombohedron and scalenohedron. In the Colonial Museum we have the following specimens:—
Calcite with Pyrites, Thames.—A massive crystalline variety with rhombohedral cleavage and small rhombohedral crystals in cavity. Colour, white.
Calcite with Natrolite, Dunedin.—Small rhombohebral crystals R, and also acute rhombohedrons in cavity in basaltic rock. Colour, pure white and transparent, to dirty grey.