How can you tell the difference between plagioclase and alkali feldspar in thin section?
Alkali feldspars can often be distinguished from plagioclase feldspars because most grains of the latter exhibit albite twinning (see above Crystal structure), which is manifested by parallel lines on certain cleavage surfaces, whereas grains of alkali feldspars do not.
What is the crystallographic difference between sanidine and microcline?
They are almost identical in physical properties, and sometimes it is impossible to distinguish one another without x-ray analysis. The only difference between them is their crystal structure. Microcline crystallizes in the triclinic system, and Orthoclase and Sanidine crystallize in the monoclinic system.
What is the difference between microcline and orthoclase?
The only difference between them is their crystal structure. Crystals of Microcline are generally much larger than those of Orthoclase, and a deep green color is tell-tale sign of Microcline, since Orthoclase does not exist in a deep green color.
What color is Microcline?
Smith College – Geology 222b – Petrology Petrographic Data
| Microcline | ||
|---|---|---|
| Property | Value | Comments |
| Crystal Habit | Massive, tabular or short prismatic crystals | Forms largest known crystals. |
| Cleavage | (001) perfect (010) good at an angle of 90.6 degrees | . |
| Color/Pleochroism | White to pale yellow Colorless in thin section | No pleochroism. |
How do you identify a Microcline in the thin section?
Microcline is often characterized by a distinctive plaid (cross-hatched) twinning (also known as tartan twinning), giving a zebra stripe appearance. This type is also called gridiron or quadrille structure, the two sets or lamellae being at right angles.
What is the difference between plagioclase feldspar and potassium feldspar?
The feldspars are divided into two main groups: Potassium feldspar (“K-spar”) and plagioclase (“plag”). Both display two cleavages and an overlapping range of colors, but only plagioclase displays tiny grooves on one cleavage known as striations. Note the two cleavage surfaces and one fracture surface.
Does Microcline have fracture or cleavage?
| Microcline | |
|---|---|
| Cleavage | Has perfect cleavage parallel to {001} and good cleavage on {010}. Cleavages intersect at 90°41′. It can be difficult to see cleavage in thin section due to microcline’s low relief. |
| Fracture | Uneven |
| Tenacity | Brittle |
| Mohs scale hardness | 6-6.5 |
How do you identify a microcline in the thin section?
Does microcline have fracture or cleavage?
How do you identify microcline?
Microcline may be clear, white, pale-yellow, brick-red, or green; it is generally characterized by cross-hatch twinning that forms as a result of the transformation of monoclinic orthoclase into triclinic microcline….
| Microcline | |
|---|---|
| Mohs scale hardness | 6-6.5 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent, translucent |
Can microcline be pink?
Physical Properties of MicroclineHide Colour: White, grey, greyish yellow, yellowish, tan, salmon-pink, bluish green, green.
Where is Sanidine found?
felsic volcanic rocks
Sanidine is found most typically in felsic volcanic rocks such as obsidian, rhyolite and trachyte. Sanidine crystallizes in the monoclinic crystal system.
What is the difference between microcline and sanidine and orthoclase?
Sanidine forms at high temperatures and has a disordered monoclinic symmetry, whereas Orthoclase forms at low temperatures and cools slowly, forming more ordered monoclinic crystals. In some mineral reference guides, Microcline and Sanidine are wrongly categorized as variety of Orthoclase.
What is sansanidine microcline?
Sanidine is a polymorph of alkali feldspar stable at yet higher temperature. Microcline may be clear, white, pale-yellow, brick-red, or green; it is generally characterized by cross-hatch twinning that forms as a result of the transformation of monoclinic orthoclase into triclinic microcline.
Is sanidine a monoclinic or triclinic polymorph?
Sanidine crystallizes in the monoclinic crystal system. Orthoclase is a monoclinic polymorph stable at lower temperatures. At yet lower temperatures, microcline, a triclinic polymorph of potassium feldspar, is stable.
What does microcline look like?
Microcline. Sanidine is a polymorph of alkali feldspar stable at yet higher temperature. Microcline may be clear, white, pale-yellow, brick-red, or green; it is generally characterized by cross-hatch twinning that forms as a result of the transformation of monoclinic orthoclase into triclinic microcline.