AMETHYST 'TWINNING' STONE BRAZIL 3.85 CTS [ST6731]

SEDA GEMS

AMETHYST TWINNING STONE

This is a natural stone which has some interesting lines in it from its formation.

Mined in Brazil.

Well polished

Nice collectors stone.

Weight 3.85 cts app

Size 11 x 4 mm app

TWINNING

Twinning form as a result of an error during crystallization. Instead of a "normal" single crystal, twins will often appear doubled where two crystals appear to be growing out of or into each other, like Siamese twins. Some twins however are not even identifiable outwardly and some minerals in fact have been found to be just a twinned variety of another mineral. Accidental relationships are not considered twins, such as when two distinct crystals grow more or less randomly side-by-side or toward each other, etc. Also epitaxial overgrowths are also not twins. These occur when one mineral of similar structure, but different chemistry, grows onto and "continues" the earlier mineral's crystal.. Twins are recognized by penetration angles or notches in the crystal, mirror planes that do not normally occur on a specific mineral and crystallographic techniques not normally available to the average collector. Twinning often has a dramatic effect on the outwardsymmetry  of the mineral either by raising or lowering the symmetry. Twinning can make an orthorhombic mineral appear hexagonal or make a trigonal mineral appear monoclinic.

 Amethyst  is  a purple form of quartz and it is the Birthstone  associated with February..Amethyst occurs in primary hues from a light slightly-pinkish violet to a deep grape purple. Amethyst may exhibit one or both secondary hues, red and/or blue. The ideal grade is called "Deep Siberian" and has a primary purple hue of around 75–80 percent, 15–20 percent blue and (depending on the light source) red secondary hues