Ruby
The English name "ruby" comes from the Latin word *ruber* (meaning "red stone") and was originally a general term for red gemstones. Rubies are corundum that has been colored red due to the presence of chromium (Cr), which has the characteristic of preventing the crystal from growing very large. Furthermore, Cr emits a red fluorescence under ultraviolet light, which is often described as "looking like burning coal."
A gemstone whose evaluation centers on its red color and fluorescence caused by Cr
Basic Information
| English Name | Ruby |
|---|---|
| Japanese Name | Kogyoku |
| Chemical Formula | Al2O3 |
| Classification | Hexagonal (Trigonal) system |
| Hardness | 9 |
| Specific Gravity | 4.02 |
| Transparency | — |
Characteristics & Variations
- Color Description: Pigeon Blood (Cr-only coloration: Myanmar, marble host rock) / Oxblood (Cr + trace Fe: Thailand, basalt host rock).
- Host Rock: Marble, basalt, gneiss, amphibolite, mica schist, zoisite schist (While igneous rocks exist, they are mostly produced from metamorphic rocks).
- Star: Star Ruby (high Ti content → rutile needle crystals → star effect).
- Double Star: Twinning resulting in the six-ray star appearing as twelve (e.g., from Vietnam).
- Cat's Eye: Incomplete distribution of acicular rutile resulting in a single line (extremely rare).
- Trapiche: Six crystals arranged in a radial pattern (known from Myanmar, though often small in size).
Treatments, Similar Stones, & Related Info
Treatments: Dyeing (soaking low-quality stones in red dye), heat treatment (adjusting black or purple tints derived from Fe/Ti), filling (filling cracks/cavities with fillers during heating to hide defects).
Similar Stones: Red spinel, pyrope (chrome pyrope), rubellite (tourmaline), eudialyte, etc. The key to identification is their overwhelming hardness.
Related Info: Synthesized via the Verneuil process, flux method, or hydrothermal method; some are so sophisticated that even gemological laboratories find them difficult to distinguish from natural stones.
Note: In the market, "treatments (heating/filling)" significantly affect quality and price. If describing them, the standard approach is the triad of: color name (Pigeon/Ox) + host rock + treatment.