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.

What is twin crystals in crystallography?

twinning, in crystallography, regular intergrowth of two or more crystal grains so that each grain is a reflected image of its neighbour or is rotated with respect to it. Other grains added to the twin form crystals that often appear symmetrically joined, sometimes in a starlike or crosslike shape.

What is twin law?

The twin law is the set of twin operations mapping two individuals of a twin. It is obtained by coset decomposition of the point group of the twin lattice with respect to the intersection group of the point groups of the individuals in their respective orientations.

What causes polysynthetic twinning?

Polysynthetic twinning – occurs when three or more individuals are repeated alternately on the same twinned plane. If the individuals of polysynthetic twins are thin plates, the twinning is called lamellar e.g. plagioclase feldspars.

What does Pericline mean?

Definition of pericline 1 : a variety of albite occurring in white opaque crystals elongated in the direction of the macro-axis and often twinned with this axis as twinning axis. 2 : one of the layers making up a periclinal chimera. 3 : a periclinal cell wall.

What is Pseudomorphism in geology?

Pseudomorphism is the existence of a mineral that has the appearance of another mineral. Pseudomorph means false form. Pseudomorphism occurs when a mineral is altered in such a way that its internal structure and chemical composition is changed but its external form is preserved.

What causes twinning in crystals?

Transformation Twins – Transformation twinning occurs when a preexisting crystal undergoes a transformation due to a change in pressure or temperature. This commonly occurs in minerals that have different crystal structures and different symmetry at different temperatures or pressures.

What states have twin laws?

Currently, 14 states have twin laws on the books, while no less than 11 others have legislation pending or sponsored bills awaiting review….The states with enacted laws are:

• Arkansas.
• Florida.
• Georgia.
• Illinois.
• Louisiana.
• Maryland.
• Massachusetts.
• Mississippi.

What are types of twins?

There are two types of twins – identical (monozygotic) and fraternal (dizygotic). To form identical twins, one fertilised egg (ovum) splits and develops two babies with exactly the same genetic information.

What is polysynthetic twin?

Contact twins can also occur as repeated or multiple twins. If the compositions surfaces are parallel to one another, they are called polysynthetic twins. Plagioclase commonly shows this type of twinning, called the Albite Twin Law, with {010} as the twin plane.