Feldspar is restricted to the ground mass . Outcrops of the lamprophyres, which can usually be traced for less than 500 feet, range in width from 2 to 25 Ieet. Received 1 October 1990, accepted 1 August 1991 Key words: alkaline dyke, geochemistry, lamprophyre, mineralogy, petrology Introduction There are many different rocks grouped under the heading lamprophyre. Any of a heterogeneous group of gray to black, mafic igneous rocks characterized by a distinctive panidiomorphic and porphyritic texture in which abundant euhedral, dark-colored ferromagnesian (femic) minerals (dark mica, amphibole, pyroxene, olivine) occur in two generations—both early as phenocrysts and later in the matrix or groundmass—while felsic minerals … Is a melilitic lamprophyre that usually contain between 10-30% of feldspathoids (Nepheline and Hauyne) and it normally contains the same minerals as occur in alnöite. Lamprophyre rocks are melanocratic or mesotype rocks hypabyssal rocks. The hornblende and biotite are brown or greenish-brown, and as a rule their crystals even when small are very perfect and give the lamprophyre may and often does contain all four minerals but is named according to the two which predominate. Gem sapphires also occur as xenocrysts in alkaline basic lamprophyre such as for the Yogo Gulch deposit in Montana (Brownlow and Komorowski, 1988; Renfro et al., 2018), as mafic dikes of biotite monchiquite called ouachitite, a lamprophyre characterized by an abundance of phlogopite and brown amphibole, olivine, clinopyroxene, and analcime. They are normally rich in alkalis, volatiles, Sr, Ba and Ti, with biotite-phlogopite and/or amphibole phenocrysts. Their common features indicate that these widespread lamprophyre dykes all formed during the Early Cretaceous . Lamprophyre definition is - any of a series of dark rocks of basaltic habit that resemble trap, occur usually in narrow dikes, and sometimes contain glittering plates of biotite. magmas which have undergone varying but generally low degrees of polybaric fractionation, together perhaps with mixing of more primitive and fractionated batches, during their ascent through the crust. Table 19-6 Lamprophyre a diverse group of dark, porphyritic, mafic to ultramafic hypabyssal (or occasionally volcanic), commonly highly potassic (K>Al) rocks. These rocks contain also iron oxides (usually titaniferous), apatite, sometimes sphene, augite, and olivine. Alnoite; From Alno island, Sweden. They contain mafic phenocrysts in a fine-grained groundmass. The lamprophyre intrusion occurs as brecciated outcrop with angular country rock granitoid clasts and also it forms stringers/veinlets within the granitic country rock. Biotite, usually phlogopite and amphibole, usually pargasite or other magnesian hornblende are panidiomorphic; all are euhedral, well formed. Similar lamprophyres also occur in the southern Sulu area in the Jiaodong Peninsula (e.g., 120 Ma; Deng et al., 2017) and the villages of Xiaya and Jingziyu in the western Luxi area (e.g., 130 Ma; Yang et al., 2019). Lamprophyre. lamprophyre dyke swarms occur widely in the Jiaodong Peninsula and they are thus suitable for constraining the c ompositions, ori- gins, and mechanisms of mantle metasomatism (e.g., Deng et al., They generally strike at 050 to 055 degrees and dip steep to vertical, but occasionally The iamprophyres are of two types, sodic syenites and sodic diorites. They typically occur as shallow dikes, sills, plugs, or stocks. Wideiy scattered dark gray lamprophyre dikes in the Mount Rosa area strike generally north-northlvest and dip steeply. 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