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Based on their color index, rocks can be classified as melanocratic (higher color index), leucocratic (lower color index), or mesocratic (middle color index), as well as hololeucocratic and holomelanocratic (extremes to either side). [1] For example, leucocratic granite would be brighter and have a lower color index than regular granite. [1]
When using the chart, it is important to remember these tips: Isotropic and opaque (metallic) minerals cannot be identified this way. The stage of the microscope should be rotated until maximum colour is found, and therefore, the maximum birefringence. Each mineral, depending on the orientation, may not exhibit the maximum birefringence.
Monzogranite – Biotite granite rocks that are considered to be the final fractionation product of magma – A silica-undersaturated granite with <5% normative quartz; Monzonite – Igneous intrusive rock with low quartz and equal plagioclase and alkali feldspar – a plutonic rock with <5% normative quartz
^ Colorado is the only state whose geological symbols reflect the national flag's colors: red (rhodochrosite), white (yule marble), and blue (aquamarine). ^ Florida's state gem, moonstone, was adopted to highlight Florida's role in the United States' Lunar program, which landed the first astronauts on the Moon. [81]
PDF version of the chart. The colors of the chart were described by McCamy et al. with colorimetric measurements using the CIE 1931 2° standard observer and Illuminant C, and also in terms of the Munsell color system. Using measured reflectance spectra, it is possible to derive CIELAB coordinates for Illuminants D 65 and D 50 and coordinates ...
The biotites in I-type granites are greener in general than those in S-type, both in hand sample and in plane polarized light. More mafic composition granites, those with a higher color index, contain more hornblende and biotite. [1] Hornblende is a typical I-type granite mineral which never occurs in S-type granite.
Higher color indices correlate with higher plagioclase to alkali feldspar ratios. [7] The most common high color index mineral in an S-type granite is biotite. [1] [4] Figure 7. Cross-polarized light photomicrograph of sample CV-114 from the S-type Strathbogie Granite with quartz and feldspar displaying a granophyric texture.
Jasper, an aggregate of microgranular quartz and/or cryptocrystalline chalcedony and other mineral phases, [1] [2] is an opaque, [3] impure variety of silica, usually red, yellow, brown or green in color; and rarely blue. The common red color is due to iron(III) inclusions. Jasper breaks with a smooth surface and is used for ornamentation or as ...