Tigereye

Scientific:
Tigereye is a quartz pseudomorph (replacement) after riebeckite. It is a minor gemstone and is not very valuable. However, because it is so desirable, it would be more valuable if it were not so abundant. The hawk's eye variety is more rare and therefore more expensive. Tigereye is light to dark brown with lustrous yellow to brown parallel fibrous inclusions. It is vitreous (hard, un-bendable, glasslike). It has strong chatoyancy (light reflection that moves when the stone is moved or seen from different angles). Its fibers are twisted or crumpled instead of straight and are a reminder of sand and sunlight.

Tigereye, hawk's eye, bull's eye quartz and cat's eye quartz only differ in their ground (background) colors and that of their mobile reflections. In this family of tigereye, when the ground color is greenish-gray or green, the gem is known as cat's eye quartz. If the ground is blue-gray or bluish, the gem is known as hawk's eye. A golden yellow reflection on a brown or black ground is known as tigereye. A stone with a mahogany color ground is called bull's eye or ox eye. Red tigereye is not natural; it is usually heated which oxidizes the iron and turns it red.

There is a huge difference in appearance between rough and polished tigereye. These gemstones are usually cut in a cabochon (cut curved on top with a flat bottom), which brings out the chatoyancy, the stones main characteristic. Cutting it into rounded shapes brings out this mobile reflection. When cut into larger objects this chatoyancy shows up in stripes.

Tigereye comes principally from South Africa. It comes in polished shapes because of government restrictions that forbid the export of raw materials. Raw (uncut) tigereye displays no chatoyancy. Tigereye is also found in Australia, Burma, Namibia and California in the USA.

History: 
Tigereye made its gemstone debut sometime in the late 19th century. Interestingly, it fetched several dollars per carat back then. A 1932 German book on gemstones (Bauer and Schlossmacher, 1932, 674) states that in about 1880, tigereye sold for 25 to 39 Marks per carat, or between $6.25 and $7.50 per carat - at a time when western American miners usually fought in vain to earn $3.50 for a hard, dangerous, 10-hour day underground in rich gold and silver mines. 

The word "Tigereye" is currently preferred by Americans and "Tiger's-eye" by people or other English speaking countries (as Anglophiles might say). In the past, American publications have used a hyphen in both tiger-eye and tiger's-eye; the South African government refers to it as the latter. An earlier but now discarded term, griqualandite, has also been used as a synonym for tigereye. 
- from http://www.lapidaryjournal.com

Myth:
Traditionally, tigereye has been favored as a gift between lovers. It is said to ease sexual tension and help partners tune in to each other in a psychic or telepathic way.