Amethyst
Amethyst is a variety of quartz, and the word means "not drunk" in Greek. It can be found in many places throughout the world, including most U.S. states. The color of this crystal varies from a light, clear purple to a deeper purple shade. The gem is called elusive, which means that it will eventually fade in color. Six months of daily exposure to sunlight will fade an amethyst crystal to a very pale purple color, and sometimes can even leave behind a gray-looking quartz.
Kunzite
Kunzite is a pink or lilac crystal that is part of the spodomene group. It was named after Frederick Kunzite, who discovered the crystal in California in 1902. It can be found in Africa, Brazil, Canada, the USA, Madagascar, Mexico and Sweden. The crystal is heated to enhance the light pink color to a darker shade, and this particular crystal has an ability to absorb sunlight. Due to this absorbing talent, it is sometimes referred to as the "evening stone" because it is a crystal that shouldn't be worn during the day, only in the evening. You should avoid wearing this crystal during the day because when it absorbs sunlight the color of the crystal fades.
Citrine
Citrine is a type of quartz that ranges in color from pale yellow to light brown. Visually it is often confused with yellow topaz, but the two crystals differ in their hardness. It is rare to find citrine in nature. Instead, most commercial citrine is heat-treated amethyst or smoky quartz. These artificially produced citrine crystals tend to have more of an orange or reddish cast compared to the pale yellow ones that are found naturally. Like amethyst, citrine will fade after prolonged exposure to sunlight and heat. Because of this, citrine jewelry and crystals should not be regularly worn or hung in the sun.
Brown Topaz
Brown topaz will fade rapidly when exposed to the sun and light. It has even been reported to have lost color between the mining site and the mine entrance. It is found in Nigeria, Sri Lanka, Russia, Burma, the USA and Mexico. It is a fluorine aluminium silicate and has a distinct brown color. This crystal should only be worn in the evening and should be stored in a dark place when not being used.