Though perhaps best known as inclusions within other gems, rutile crystals themselves can be faceted or cabbed as curiosities for collectors. Rutile can show a deep, red color. Synthetics can show a variety of colors and have even been used as diamond simulants.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Crystallography||Tetragonal. Crystals prismatic, vertically striated, well developed, often twinned into a series of contact twins with up to eight individuals, sometimes looping to form a complete circle! Also, massive; granular.|
|Colors||Black, deep red, brownish red. Greenish (if Nb present), also bluish and violet. A variety rich in Cr is deep green.|
|Luster||Metallic to adamantine.|
|Fracture||Conchoidal to uneven. Brittle.|
|Hardness||6 - 6.5|
|Specific Gravity||4.23, also see "Identifying Characteristics" below.|
|Cleavage||Distinct 1 direction.|
|Transparency||Transparent to opaque.|
|Formula||TiO2 + Nb, Ta, Fe.|
|Pleochroism||Distinct: shades of red, brown, yellow, green.|
|Optics||o = 2.62; e = 2.90. Uniaxial (+). Sometimes anomalously biaxial.|
|Etymology||From the Latin rutilus for red, in allusion to the color.|
|Occurrence||In addition to its occurrence as inclusions in other minerals, occurs as a high-temperature mineral, in gneiss and schist, also in alpine-type veins; found in igneous rocks, pegmatites, regionally metamorphosed rocks, including crystalline limestones, and as detrital grains.|
Rutile crystals occur as needle inclusions in a wide variety of gem materials, such as quartz (rutilated quartz) and agate (sagenite). In corundum, they occur as fibers, causing asterism in stones such as star sapphires. Rutile inclusions also cause chatoyancy in gem materials such as chrysoberyl.
Faceted rutiles may disappoint collectors because the finished gems are so dark. Rutile’s deep, red color may be so intense it can’t be seen easily in stones larger than 1 carat. Cabochons might show reddish reflections in cracks and along imperfections.
Swiss rutile seems a bit more transparent than material from other localities.
Rutile’s specific gravity varies somewhat in relation to its trace elements.
- Iron (Fe) bearing: 4.2 – 4.4.
- Niobium (Nb) and tantalum (Ta) bearing: 4.2 – 5.6.
Synthetic rutiles appeared on the gem market in 1948. Created through the Verneuil or flame fusion process, these synthetics can show colors such as yellow, brown, red, and blue. Near colorless stones with a yellow tinge can take full advantage of rutile’s high dispersion, six time greater than diamond. For a time, gem dealers sold synthetic rutiles under the name “Titania” as diamond simulants. However, these stones showed too much fire to be believable simulants. They faded from use as other diamond simulants emerged, such as cubic zirconia.
Heat treatments can turn light yellowish synthetic rutiles blue.
Sierra Leone produces nearly a third of the world’s supply of rutiles.
Graves Mountain, Georgia produces fine rutile crystals in quartz veins. These pieces can weigh up to several pounds.
Other notable gem-quality sources include:
- Magnet Cove, Arkansas: huge, rough crystals.
- California; North Carolina; South Dakota; Virginia.
- Brazil: large, fine crystals.
- France; Russia; Switzerland.
Large crystals often have transparent areas that can provide stones for faceting. However, cut rutiles above 2-3 carats are so dark they appear opaque. Thus, this becomes the effective size limit of faceted gems.
- Devonian Group (Calgary, Alberta, Canada): 3.70.
You’re more likely to find natural rutiles in mineral collections than in jewelry collections. If you do have a synthetic gem as a diamond simulant, keep in mind that while it may exceed diamond in dispersion, it’s far less hard (6 – 6.5). Store it separately from other common jewelry stones such as quartz and topaz to avoid contact scratches. For cleaning, use a soft brush, mild detergent, and warm water. Consult our gemstone jewelry cleaning guide for more recommendations.