Rutilated quartz is a variety of

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...

which contains acicular (needle-like)

inclusion Inclusion or Include may refer to: Sociology * Social inclusion, aims to create an environment that supports equal opportunity for individuals and groups that form a society. ** Inclusion (disability rights), promotion of people with disabiliti ...

s of

rutile Rutile is an oxide mineral composed of titanium dioxide (TiO2), the most common natural form of TiO2. Rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest refractive indices at visib ...

. It is used for gemstones. These inclusions mostly look golden, but they also can look silver, copper red or deep black. They can be distributed randomly or in bundles, which sometimes are arranged star-like, and they can be sparse or dense enough to make the quartz body nearly opaque. While otherwise inclusions often reduce the value of a crystal, rutilated quartz is valued for the quality and beauty of these inclusions.''Nature Guide – Gems'', E-Book, Dorling Kindersley 2013, p. 108

References

4. Reference to rutilated quartz in "Closer to the Heart", Mercedes Lackey, Author. Minerals Quartz varieties Dielectrics Piezoelectric materials Trigonal minerals Luminescent minerals Quartz gemstones {{mineral-stub