Inclusions in Quartz are Extremely Common
Also Known as Included Quartz
Inclusions in quartz are relatively common. They can be air, water, tar, petroleum or any number of other substances. Rutile and tourmaline are two of the most common mineral inclusions (in quartz).
Rutile is known for its needle-like crystals which are made up primarily of titanium dioxide. They grow naturally within quartz crystals over millions of years. The inclusions often resemble fine strands of hair. For this reason they're sometimes known as Venus hair or Cupid's darts.
Although these stones were once known as sagenite, the name is now rarely used. Today they tend to be known as rutilated quartz or golden rutile. The name black rutile is often used when the inclusions are black.
The colour of rutile crystals can vary from pale yellow to rich orange to reddish brown. They can also be black. Black inclusions are often mistaken for tourmaline. Rutile and tourmaline are two completely different minerals.
Quartz included with crystals of tourmaline is known as tourmalinated quartz.
Rutilated quartz and tourmalinated quartz are widely used for gemstones. Stones may be faceted but cabochons are more common.
The density of the crystal inclusions can vary dramatically. Whilst some stones are only lightly included others are full to capacity. When heavily included the quartz can look almost opaque. The stone's colour will often be heavily influenced by the colour of the inclusions.
The colour of the man-made material known as goldstone is also influenced by its inclusions. The glass used to produce this stone is clear but the crystallised copper gives it an orange-brown colour.
Rubies and sapphires can also be included with rutile. In some instances the reflectance of light off the crystal inclusions causes an optical phenomenon known as asterism. This is best seen in stones that are shaped as a cabochon.
Where asterism is present the gemstone becomes known as star ruby or star sapphire. This is 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. A spangled or subtle sparkly effect can be seen on the surface of the stone caused by the reflection of light. This optical phenomenon is known as aventurescence.
The rutilated quartz in our first picture is on display in the Smithsonian Museum of Natural History, Washington D.C. Photo by Stone Mania. The photo is clickable and redirects to the original non-compressed image.