Polishing the stone or cleaning it by ultrasonic or steamer must be done with caution. See also
Ametrine
List of minerals
Specimen Ridge Minerals portal

References

Kostov, R. I. 1992. Amethyst. A Geological-Mineralogical and Gemmological Essay. Union of Scientists in Bulgaria, Sofia, 249 p. (in Bulgarian with English abstract)
Lieber, W. 1994. Amethyst. Geschichte, Eigenschaften, Fundorte. Christian Weise Verlag, München, 188 S.
Coats disease is a rare congenital, nonhereditary eye disorder, causing full or partial blindness, characterized by abnormal development of blood vessels behind the retina. Coats disease can also fall under glaucoma. It can have a similar presentation to that of retinoblastoma. Signs and symptoms
The most common sign at presentation is leukocoria (abnormal white reflection of the retina). Symptoms typically begin as blurred vision, usually pronounced when one eye is closed (due to the unilateral nature of the disease). Often the unaffected eye will compensate for the loss of vision in the other eye; however, this results in some loss of depth perception and parallax. Deterioration of sight may begin in either the central or peripheral vision. Deterioration is likely to begin in the upper part of the vision field as this corresponds with the bottom of the eye where blood usually pools. Flashes of light, known as photopsia, and floaters are common symptoms. Persistent color patterns may also be perceived in the affected eye. Initially, these may be mistaken for psychological hallucinations, but are actually the result of both retinal detachment and foreign fluids mechanically interacting with the photoreceptors located on the retina. One early warning sign of Coats disease is yellow-eye in flash photography. Just as the red-eye effect is caused by a reflection off blood vessels in the back of a normal eye, an eye affected by Coats will glow yellow in photographs as light reflects off cholesterol deposits.