How do you identify a feldspar in a thin section?
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How do you identify a feldspar in a thin section?
In general, keys to identifying K-feldspar are its (lack of) color, its low birefringence, and its twinning. In thin section, microcline, orthoclase and sanidine are distinguished by their twinning, optical sign, and 2Vo.
How can you tell the difference between feldspar and quartz?
Quartz is a mineral compound containing silicon and oxygen atoms, and feldspar is a mineral compound containing mainly aluminum, silicon, and oxygen atoms. Therefore, the key difference between quartz and feldspar is that the major chemical element present in quartz is silicon whereas in feldspar it is aluminum.
What is the properties of feldspar?
| Generalized Physical Properties of Feldspar Minerals | |
|---|---|
| Chemical Classification | Silicate |
| Mohs Hardness | 6 to 6.5 |
| Specific Gravity | 2.5 to 2.8 |
| Diagnostic Properties | Perfect cleavage, with cleavage faces usually intersecting at or close to 90 degrees. Consistent hardness, specific gravity and pearly luster on cleavage faces. |
What are the two most common types of feldspar?
The feldspars are divided into two main groups: Potassium feldspar (“K-spar”) and plagioclase (“plag”).
How do we identify plagioclase feldspar?
It is usually easy to distinguish plagioclase feldspars because their two planes of cleavage intersect at 90-degree angles, and their cleavage faces often display striations. These properties make plagioclase feldspars relatively easy to identify with a hand lens in coarse-grained igneous and metamorphic rocks.
What is the texture of feldspar?
Feldspars are slightly translucent and have a glassy, or vitreous, luster rather like that of glazed porcelain. Because their atomic framework has planes of weakness, feldspars exhibit good cleavage, breaking readily into blocky pieces with smooth sides.
What is the difference between geodes and feldspar?
is that geodes is while feldspar is (mineral) any of a large group of rock-forming minerals that, together, make up about 60\% of the earth’s outer crust the feldspars are all aluminum silicates of the alkali metals sodium, potassium, calcium and barium feldspars are the principal constituents of igneous and plutonic …
How can you tell the difference between halite and calcite?
Calcite and halite are mineralogical names. The key difference between calcite and halite is that the calcite is the mineral form of calcium carbonate, whereas the halite is the mineral form of sodium chloride. Therefore, the chemical formula for calcite is CaCO3 and chemical formula of halite it is NaCl.
How do you identify amphibole?
Long prismatic, acicular, or fibrous crystal habit, Mohs hardness between 5 and 6, and two directions of cleavage intersecting at approximately 56° and 124° generally suffice to identify amphiboles in hand specimens. The specific gravity values of amphiboles range from about 2.9 to 3.6.
What is the classification of feldspar?
In the classification of igneous rocks of the International Union of Geological Sciences (IUGS), the feldspars are treated as two groups: the alkali feldspars and the plagioclase feldspars. The alkali feldspars include orthoclase, microcline, sanidine, anorthoclase, and the two-phase intermixtures called perthite.
What does plagioclase feldspar look like?
It is usually easy to distinguish plagioclase feldspars because their two planes of cleavage intersect at 90-degree angles, and their cleavage faces often display striations. Plagioclase in granitic rocks is normally white, pink, or red in color. In basaltic rocks it is normally gray to black.
What does halite look like?
Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, pink, red, orange, yellow or gray depending on inclusion of other materials, impurities, and structural or isotopic abnormalities in the crystals.