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Like others of the series, bytownite forms grey to white triclinic crystals commonly exhibiting the typical plagioclase twinning and associated fine striations. The specific gravity of bytownite varies between 2.74 and 2.75. The refractive indices ranges are nα=1.563 – 1.572, nβ=1.568 – 1.578, and nγ=1.573 – 1.583.
Plagioclase displaying cleavage. (unknown scale) In volcanic rocks, fine-grained plagioclase can display a "microlitic" texture of many small crystals. Plagioclase (/ ˈ p l æ dʒ (i) ə ˌ k l eɪ s, ˈ p l eɪ dʒ-,-ˌ k l eɪ z / PLAJ-(ee)-ə-klayss, PLAYJ-, -klayz) [4] is a series of tectosilicate (framework silicate) minerals within the feldspar group.
Merohedral twinning occurs when the lattices of the contact twins superimpose in three dimensions, such as by relative rotation of one twin from the other. [8] An example is metazeunerite. [9] Contact twinning characteristically creates reentrant faces where faces of the crystal segments meet on the contact plane at an angle greater than 180°. [3]
Labradorite ((Ca, Na)(Al, Si) 4 O 8) is a calcium-enriched feldspar mineral first identified in Labrador, Canada, which can display an iridescent effect ().. Labradorite is an intermediate to calcic member of the plagioclase series.
The composition of plagioclases is often expressed as a molar percentage of An%, or (for a specific quantity) An n, where n = Ca/(Ca + Na) × 100. [8] This equation predominantly works in a terrestrial context; exotic locales and in particular Lunar rocks may need to account for other cations, such as Fe 2+ , to explain differences between ...
This combination leads to a grid pattern, hence microcline displays gridiron twinning. Can also display carlsbad twinning, simple twins, or lack twinning altogether. Lamellae in microcline are discontinuous and "pinch and swell". Photomicrograph of thin section of microcline showing crosshatched crystal twinning (in cross polarized light) Cleavage
Nearby is a sacred water-filled sinkhole called a cenote, where the bodies of more than 200 people were found. And close to that is the chultun where the boys were buried. "The original purpose of ...
Oligoclase is a rock-forming mineral belonging to the plagioclase feldspars. In chemical composition and in its crystallographic and physical characters it is intermediate between albite (Na Al Si 3 O 8) and anorthite (CaAl 2 Si 2 O 8). [1] The albite:anorthite molar ratio of oligoclase ranges from 90:10 to 70:30.