著者

青木 義和

出版者

Japan Association of Mineralogical Sciences

雑誌

岩石鉱物鉱床学会誌 (ISSN:00214825)

巻号頁・発行日

vol.77, no.Special3, pp.123-128, 1982 (Released:2012-08-03)

参考文献数

10

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Large numbers of [100], [110] and [111] penetration twins are formed during growth of KC1 crystals from solution. All of them are interpenetrating octahedrons with rotation of some angles about [100], [110] and [111] common axis of two individuals, respectively. Twin formation appeared to be favored by Pb2+ and relatively high supersaturation. The maximum yield of twins is obtained at the region of 0.4-0.6 g Pb2+/l H2Oand σ=0.1-0.4. The formation is discussed in terms of rotation twinning, on the basis of the concept of coincidence-site lattices. Good agreement is obtained between the angles of some crystallographic directions observed in the twins and those expected from this concept.

著者

青木 義和 肥田 昇

出版者

The Society of Resource Geology

雑誌

鉱山地質 (ISSN:00265209)

巻号頁・発行日

vol.24, no.125, pp.201-211, 1974-06-30 (Released:2009-06-12)

参考文献数

23

被引用文献数

4

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Mihara mine, Hiroshima Prefecture, had been exploited for dissemination fluorite deposits in skarn and monzonite. Rocks of this area consist of Paleozoic limestone, chert and diabasic rocks intruded by Cretaceous biotite granite. The Paleozoic formation is thermally metamorphosed and metasomatised by the granite which is partly monzonitised. Fluorite ores occur in the monzonite and adjacent skarns.Recently presence of beryllium mineralization in this ore deposit was discovered with a beryllium detector. The mineralization occurs mostly in the monzonite and partly in the scheelite-feldspars-fluorite-iron-rich biotite skarn. The beryllium mineral contained in the skarn is exclusively phenacite which coexists with iron-rich biotite, plagioclase and potassium feldspar, filling the grain boundaries of fluorite crystals. A small amount of scheelite is also found in association with the minerals. On the other hand, danalite is the main beryllium mineral in the monzonite. It occurs as disseminated grains of euhedral or subhedral form, and is associated with violet fluorite and feldspars. Phenacite is also present in a trace amount. It is conspicuous that these phenacites are always corroded along cleavages and cracks, and also surrounded by danalite grains.Volumetric analyses of constituent minerals in thin sections by a point counter reveal that (1) danalite and phenacite are found in specific monzonite which contains fluorite and quartz more than 5.6% and less than 2.3%, respectively; (2) the quantity of modal danalite in such rocks ranges from 2.5% to 3.6%, and that of phenacite is less than 0.4%; and (3) the amount of quartz gradually decreases towards the adjacent skarn body, while total feldspars and fluorite increase in contrast. The degree of Al/Si order-disorder and the Or contents in potassium feldspars in biotite granite and monzonite were determined with powder X-ray diffractometry. Potassium feldspars in biotite granite have a tendency to become ordered and rich in Or component with coming close to monzonite, and the maximum ordering and Or contents are encountered where they coexist with danalite in monzonite. These results are correlative with the modal analysis data.From the results obtained, the genesis of this beryllium ore deposit may be summarized as follows : (1) Paleozoic rocks were partly metasomatised by the intrusion of Cretaceous biotite granite. (2) Migration of silica from the granite to the adjacent skarn body caused relative increases of alkali and alumina contents in peripheries of the granite, converting them to monzonite. (3) Only a small portion of beryllium contained in the granite could have moved to the skarn body to form phenacite at a limited part of the skarn. (4) The main portion of beryllium was precipitated as danalite crystals within the monzonite.