Quartz with Inclusions, aka Included Quartz

Rutilated and Tourmalinated Quartz

Inclusions in quartz, which are relatively common, can include trapped gases, water, petroleum, or other minerals. 

Rutile and tourmaline are the two most common mineral inclusions.

Rutile is known for its needle-like crystals, composed primarily of titanium dioxide. These crystals, which grow within the quartz over millions of years, resemble fine strands of hair. For this reason, they're sometimes called Venus hair or Cupid's darts.

Although rutilated quartz was once known as sagenite, this name is now rarely used. Today, it's known as rutilated quartz or included quartz.

Rutile crystals can vary in colour from pale yellow to a rich orange to reddish-brown and can also be black. When the crystals exhibit a yellow or golden colour, the quartz may be known as golden rutile. When they're black, the name black rutile is often used.

Inclusions of black rutile can be mistaken for tourmaline. Quartz included with tourmaline is known as tourmalinated quartz. Tourmaline and rutile are two different minerals.

Both rutilated and tourmalinated quartz are widely used for gemstones. Although sometimes faceted, cabochons are more common. 

The density of the crystal inclusions can vary dramatically. Some included quartz may only have a few inclusions, while other stones may be densely packed. When heavily included, the quartz can appear almost opaque.

The colour of the crystal inclusions often influences the colour of the quartz.

Goldstone, which is man-made, is produced with clear, colourless glass. However, the inclusions of crystallised copper are responsible for the stone's orange-brown colour.  

Rubies and sapphires can also feature rutile inclusions. In some gemstones, light reflecting off these crystal inclusions produces an optical phenomenon known as asterism. This effect is best seen in stones shaped as a cabochon.

Where asterism is present, the gemstone becomes known as a star ruby or star sapphire because a star-like reflection can be seen.

Aventurine is another variety of included quartz. The microscopic inclusions in aventurine are mostly mica or hematite. Stones have a spangled or subtle sparkly appearance caused by light reflecting off the metallic inclusions. This effect is known as aventurescence.

Article Photos

The rutilated quartz in our first picture is in the Smithsonian Museum of Natural History, Washington, D.C. Photo: Stone Mania.

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Rutilated quartz: Courtesy of James St. John.