To a Westerner, the idea that certain crystals have special properties sounds distinctly New Age. In Taiwan, it's widely accepted that a bracelet made of clear crystal can boost the wearer’s powers of concentration and memorization; that turquoise helps one recover from surgery; and that yellow crystal attracts unearned wealth (such as lottery winnings) while also protecting the lungs (it's popular with smokers as a result).
Rose quartz is a love stone. If worn as part of a bracelet, it indicates the wearer is searching for love. Presenting a piece of rose quartz to a member of the opposite sex is a declaration of affection. A rose quartz sphere placed in the matrimonial bedroom should enhance a couple's sex life. Topaz is said to bring you love and happiness, and help you avoid accidents (fires in particular). Lapis lazuli is often given to children as it's believed to aid their all-round development, while amethyst is thought to confer wisdom.
Crystal bracelets are sold in night markets, in and near temples and online. They're seldom expensive but if you're not a gemologist, it's hard to know exactly what you're being offered.