Rutilated Quartz
Microscopic inclusions of rutile in quartz, tourmaline, ruby, sapphire and other gemstones, produces light effects such as cat's eye and asterisms (stars). A beautiful stone produced by large inclusions of golden rutile needles in clear quartz is called rutilated quartz. Rutilated quartz is sometimes used as a semi-precious stone and/or for carvings. This stone is produced because at high temperatures and pressure, n(SiO2)-n(TiO2) is in a stable state but as temperatures cool and pressure eases the two separate with rutile crystals trapped inside the quartz crystals.