A key for identification of rock-forming minerals in by Andrew J. Barker

By Andrew J. Barker

Structured within the kind of a dichotomous key, reminiscent of these generic in botany, the mineral key offers an effi cient and systematic method of deciding upon rock-forming minerals in thin-section. This new angle covers one hundred fifty+ of the main mostly encountered rock-forming minerals, plus a couple of rarer yet noteworthy ones. Illustrated in complete color, with 330+ top of the range mineral photomicrographs from a global selection of igneous, metamorphic, and sedimentary rocks, it additionally presents a entire atlas of rock-forming minerals in thin-section.

Commencing with a short creation to mineral structures, and the homes of minerals in plane-polarised and cross-polarised gentle, the mineral key additionally contains line drawings, tables of mineral houses and an interference color chart, to additional reduction mineral id. To minimise the opportunity of misidentification, and let much less skilled petrologists to take advantage of the main with self assurance, the foremost has been prepared to prioritise these homes which are most simply recognised.

Designed for simplicity and simplicity of use, it really is basically geared toward undergraduate and postgraduate scholars of mineralogy and petrology, yet must also offer a worthwhile resource of reference for all working towards geologists facing rock thinsections and their interpretation.

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Ten. Fig. 21 shows examples of inclined extinction for actinolite (Fig. 21a) and ­plagioclase (Fig. 21b). When measuring extinction of multiple lamellar twinned plagioclase, look for crystals with equal illumination when in N-S position relative to cross-wires (Fig. 22b), then rotate left and right in turn (Fig. 22a-c) to measure extinction angle of each twin set. If the crystal is to be regarded as reliable for extinction angle determination, the value obtained turning left should be the same or very close to the value obtained when turning right.

23b for length-fast crystals. Also note the three crystals of andalusite (var. chiastolite) in Fig. 24b, the NW-SE oriented crystal (centre) showing the high colour, the NE-SW crystal (right) showing the low colour, and the horizontal crystal (left edge), oblique to insertion direction (and at extinction when plate was inserted) showing a colour intermediate between the two, close to that of the gypsum plate. Tourmaline (Fig. 24c) is another commonly encountered length-fast crystal, in this case producing a combined 3rd order green colour.

Brown HORNBLENDE (Oxo-HORNBLENDE)(◻) PPL Oxo-hornblende phenocryst in andesite; Plomb du Cantal, France. x100 85 Note: The black iron-oxides often seen around the edge of Oxo-hornblendes result from resorption effects. , 2013). -brn to red-brn. pleochrosim. 2V = 74–82°.  KAERSUTITE(◻) (previously called BARKEVIKITE) PPL Kaersutite phenocrysts in syenogabbro (“lugarite”); Lugar Sill, Lugar, Ayrshire, Scotland. -green-blue-grn. However, high temperature hornblendes may be green to brown, or brown pleochroic.

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