What kind of twinning does orthoclase have?
Carlsbad twinning
| Orthoclase | |
|---|---|
| Color | Colorless, greenish, greyish yellow, white, pink |
| Crystal habit | Can be anhedral or euhedral. Grains are commonly elongate with a tabular appearance. |
| Twinning | Typically displays Carlsbad twinning. Baveno and manebach twins have also been reported in orthoclase. |
Does orthoclase have twinning?
Two different twin laws, the Manebach and Baveno laws, produce crystals with one prominant mirror plane and penetrant angles or notches into the crystal. Although twinning in general is common for orthoclase, single crystals showing a perfect twin are rare and are often collected by twin fanciers.
What is albite twinning?
The Albite twin law {010} indicates that the twins make a form, the faces are parallel to the mirror plane (010), i.e. perpendicular to the b-axis. Albite twinning is so common in plagioclase, that it’s presence is a diagnostic property for identification of plagioclase when seen with crossed polarizers.
What is orthoclase used for?
Orthoclase is used in the manufacture of glass and ceramics; occasionally, transparent crystals are cut as gems. Orthoclase is primarily important as a rock-forming mineral, however, and is abundant in alkali and acidic igneous rocks, in pegmatites, and in gneisses.
Does K-feldspar have twinning?
K-feldspar is similar to quartz, but quartz lacks cleavage, lacks twinning, does not alter, exhibits undulatory extinction, and is uniaxial.
What is Carlsbad twinning?
A twinned crystal in which the twinning axis is the c axis, the operation is a rotation of 180 degrees, and the contact surface is parallel to the side pinacoid. It is quite common in the alkali feldspars. An alternative spelling is Karlsbad twin. Carlsbad twin of feldspar.
What products are made of orthoclase?
Uses of Orthoclase It is a raw material used in the production of glass, ceramic tile, porcelain, dinnerware, bathroom fixtures, and other ceramics. It is used as an abrasive in scouring powders and polishing compounds. It is also cut as a gemstone.
What are the special properties of orthoclase?
Physical Properties of Orthoclase
| Color | Colorless, greenish, greyish yellow, white, pink |
|---|---|
| Streak | white |
| Luster | Vitreous, pearly on cleavage surfaces |
| Cleavage | Has perfect cleavage on {001} and good cleavage on {010}. Cleavages intersect at 90°. It can be difficult to see cleavage in thin section due to orthoclase’s low relief. |
What are twin crystals?
Crystal twinning occurs when two or more adjacent crystals of the same mineral are oriented so that they share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals that are tightly bonded to each other.
Does plagioclase always show twinning?
Plagioclase commonly shows this type of twinning, called the Albite Twin Law, with {010} as the twin plane. Such twinning is one of the most diagnostic features of plagioclase….
| EENS 2110 | Mineralogy |
|---|---|
| Tulane University | Prof. Stephen A. Nelson |
| Twinning, Polymorphism, Polytypism, Pseudomorphism |
What is Perthitic texture?
When megascopically developed, the texture may consist of distinct pink and white lamellae representing exsolved white albite (NaAlSi3O8) in pink microcline. The intergrowths in perthite have a great variety of shapes.
What is albite law?
[′al‚bīt ‚lȯ] (crystallography) A rule specifying the orientation of alternating lamellae in multiple twin feldspar crystals; the twinning plane is brachypinacoid and is common in albite.
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 is Twin defect?
Surface defect: Twin boundaries are types of planar surface defects. The atomic arrangement on one side of a twin boundary is a mirror reflection of the arrangement on the other side. Twin boundaries occur in pairs such that the orientation change introduced by one boundary is restored by the other.