Which feldspar twin?

The feldspars – orthoclase and sanidine – are the most commonly twinned minerals in the monoclinic system. Both contact twins and penetration twins occur, and both types result from accidents during growth.

What is Pericline twinning?

Pericline twinning is a type of crystal twinning which show fine parallel twin laminae typically found in the alkali feldspars microcline. The twinning results from a structural transformation between high temperature and low temperature forms.

Does plagioclase have twinning?

Similar minerals Microcline often shows distinctive “tartan plaid” twinning, but plagioclase may have two sets of twins yielding a similar appearance. In plagioclase, the contacts between twins tend to be sharp, while in microcline they are not.

Why do crystals twin?

Annealing or transformation twins are the result of a change in crystal system during cooling as one form becomes unstable and the crystal structure must re-organize or transform into another more stable form. Deformation or gliding twins are the result of stress on the crystal after the crystal has formed.

What does twinning mean?

1 : the act of producing or giving birth to twins Rates of fraternal twinning vary from population to population, and the tendency to produce fraternal twins is genetically transmitted through the mother’s line.

What does twinning and winning mean?

“Twinning” is a new portmanteau (かばん語) of the words “Twin” and “Winning”. It means when two people have the same brilliant (目覚しい) thought or action at the same time.

What is a twinning surface?

Photo :© Fred Kruijen. Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations. A twin boundary or composition surface separates the two crystals.

What is a spinel twin?

Form of contact twinning, in which two octahedral crystals twin at the base. Named after the mineral Spinel, which often exhibits this form of twinning.

What does twinning mean on Instagram?

“Twinning”—braiding your tresses to match other hairstyles around the world, then simultaneously posting pictures of both artfully knotted heads to Instagram—is an Internet sport dominated by moms and tweens.

Where is albite most commonly found?

Albite, common feldspar mineral, a sodium aluminosilicate (NaAlSi3O8) that occurs most widely in pegmatites and felsic igneous rocks such as granites. It may also be found in low-grade metamorphic rocks and as authigenic albite in certain sedimentary varieties.

How are albite and Pericline law twinning different?

Albite and pericline Law type twinning produce stacks of twin layers that are typically only fractions of millimeters to several millimeters thick. These twinned layers can be seen as striation like grooves on the surface of the crystal and unlike true striations these also appear on the cleavage surfaces.

What are the different types of twinning in minerals?

If several twin crystal parts are aligned by the same twin law they are referred to as multiple or repeated twins. If these multiple twins are aligned in parallel they are called polysynthetic twins. When the multiple twins are not parallel they are cyclic twins.

How are annealing twins different from gliding twins?

Annealing or transformation twins are the result of a change in crystal system during cooling as one form becomes unstable and the crystal structure must re-organize or transform into another more stable form. Deformation or gliding twins are the result of stress on the crystal after the crystal has formed.

Which is crystal has the appearance of penetration twinning?

In penetration twins the individual crystals have the appearance of passing through each other in a symmetrical manner. Orthoclase, staurolite, pyrite, and fluorite often show penetration twinning. Galvanized surface with macroscopic crystalline features.