Rutile is a mineral made up primarily of titanium dioxide. Its name comes from the Latin word 'rutilus' meaning 'red' in reference to the deep red colour which can be seen in some specimens when viewed under certain light. Rutile is most well known for its needle-like inclusions within other minerals but especially in quartz. Quartz that's included with rutile is better known as rutilated quartz. Rutile can also be found in rubies and sapphires and it's the cause of a visual phenomenon known as asterism. When these gemstones are cut in a specific way, a fascinating star can be seen as light hits the stone. When this is present, they are usually referred to as star ruby or star sapphire.