| 释义 | picrite|ˈpɪkraɪt|
[f. Gr. πικρ-ός bitter: see -ite1.]
†1. Min. [a. G. picrite(s) (J. F. Blumenbach Handb. der Naturgeschichte (ed. 5, 1797) xii. 584).] = dolomite. Obs. rare.
1814T. Allen Min. Nomencl. 9 Crystallized muricalcite, bitterspath, picrite. 1836T. Thomson Outl. Min., Geol. I. 181 Calcareo-carbonate of Magnesia. Dolomite—conite—..muricalcite—pearl spar—picrite [etc.]. 1896Chester Dict. Names Min., Picrite, an obs. syn. of dolomite, bitter-spar.
2. Petrogr. Also 9 picryte, pikrite. [ad. G. pikrit (G. Tschermak 1866, in Sitzungsber. der K. Akad. der Wissensch. (Math.-Naturw. Classe) LIII. 262).] A dark ultrabasic igneous rock, commmonly hypabyssal, containing a substantial amount of olivine together with augite and other ferromagnesian minerals and a small amount of plagioclase.
1868J. D. Dana Syst. Min. (ed. 5) 258 A chrysolite rock occurring at L. Lherz, consisting largely of chrysolite, has been called Lherzolyte... Another similar rock from Moravia, called picryte, consists half of chrysolite, along with feldspar, diallage, hornblende, and magnetite. 1879Rutley Study Rocks xiii. 265 Picrite is a blackish-green crystalline rock with a compact, black matrix, containing porphyritic crystals and grains of olivine. 1882A. Geikie Text-bk. Geol. 151 Olivine Rocks... The following are the more important species:—Pikrite, a rock rich in olivine, usually more or less serpentinized, with augite, magnetite, or ilmenite, and a little brown biotite, hornblende, or apatite; [etc.]. 1931S. J. Shand Study of Rocks vii. 112 Picrites with forty to seventy-five per cent. of olivine have been described in Skye. The picrite of Tabankulu, South Africa, is composed to the extent of one-third to two-thirds of well-shaped crystals of olivine which are enclosed in larger crystals of pyroxene and felspar. 1976Mineral. Mag. XL. 683 Exposures of baked siltstone occur on top of the ridge with picrite exposed only on the scarp face... The picrite averages 50% olivine, 35% plagioclase, and 15% pyroxene with a maximum grain size of 6 mm.
Hence piˈcritic a.
1931Amer. Jrnl. Sci. CCXXI. 403 Even a picritic sub⁓basalt..exhibits some interstitial quartz. 1958Trans. R. Soc. Edin. LXIII. 459 In this paper it is proposed to use the term ‘pictritic’ to denote, in minor intrusions and lavas, an amount of forsteritic olivine considerably beyond that which normally crystallizes in basaltic magma. This amount of olivine varies between 25 and 60 per cent. 1965Carnegie Inst. Year Bk. 1964 126/2 In general, picritic lavas and hypabyssal intrusives are few in number and restricted to the lower parts of both oceanic and continental volcanic columns. 1974P. G. Harris in H. Sørensen Alkaline Rocks vi. 430/1 At pressures of about 30–40 kbar, i.e. depths below 90–100 km, the mantle mineralogy will be that of a garnet lherzolite, and there is a marked change in the first-formed liquid which is now picritic or ultrabasic. |
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