Engagement Ring Guide: Know Your Options
Looking for something besides the classic round white diamond? Our engagement ring guide will help you find the alternative gem to match your unique…
Note: these prices are for natural black diamonds. Most black diamonds on the market are treated to color. Their value is in the tens of dollars per carat.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Crystallography||Isometric; Crystals sometimes sharp octahedra, dodecahedra, and combinations with other forms. Crystals modified, often rounded and distinguished by the presence of triangular-shaped pits on octahedral faces (once believed to be due to etching, these 'trigons'' are currently believed to be a result of the growth process).|
|Colors||Colorless, gray, shades of yellow, brown, pink, green, orange, lavender, blue, black; rarely red|
|Hardness||10. Diamond is the hardest natural substance and easily scratches any other mineral. The difference in hardness between diamond and corundum (9) is very much greater than that between any other two minerals on the Mohs scale.|
|Specific Gravity||3.515; Carbonado 2.9-3.5|
|Cleavage||Perfect 1 direction (octahedral). In spite of its great hardness, diamond can be split easily along octahedral planes. This feature is useful in cutting, since cleaving a large diamond saves weeks of laborious sawing. The cleavage also makes it possible for diamonds to be chipped in wear|
|Dispersion||0.044. This high dispersion in a colorless diamond creates the "fire" that is the source of the diamond's attractiveness.|
|Stone Sizes||The largest rough diamonds ever found include the Cullinan (3106 carats, white, South Africa, 1905); the Excelsior (995.2 carats. white, South Africa, 1893), the Star of Sierra Leone (968.8 carats, white, Sierra Leone, 1972), and the Great Mogul (787.5 carats, white, India, 1650). A fine yellowish octahedron of 616 carats is on display at the Mine Museum in Kimberley, South Africa, found in 1975. The world's largest uncut diamond, an 890 carat "fancy intense golden yellow" is owned by the Zale Corp. The stone is African in origin, but from an undisclosed source. If cut, it could yield a finished stone of 600 carats, which would then become the world's largest polished diamond. The Zale diamond is the fourth largest rough ever found. The largest cut stones include: Cullinan I (530.2, white, pear shape, in the British Crown Jewels), Cullinan II (317.4, white, cushion, British Crown Jewels), Great Mogul (280.0, white, dome-shape, location unknown), Nizam (277.0, white, table-cut, was in India in 1934), Jubilee (245.35, white, cushion, privately owned, Paris), and the Orloff 189.6, white, rose-cut, Russian Diamond Fund in the Kremlin).|
|Luminescence||Many diamonds fluoresce blue to violet, with fluorescence sometimes in zones (often a result of twinning). The effect is sometimes strong enough to be visible in daylight. Yellow stones sometimes fluoresce yellow-green. Some pink diamonds from India fluoresce and phosphoresce orange. The famous Hope diamond, deep blue in color, phosphoresces deep red. Most fluorescence occurs in LW; the SW reaction is weaker and the same as LW. Many diamonds fluoresce bluish white in SW. Blue-fluorescing diamonds may phosphoresce yellow (an "afterglow" reaction). The various diamonds have been organized into types, with varying UV transparency. Type 1: Transparent to all wavelengths down to about 3000 Å; this type contains nitrogen and is further subdivided into Types Ia and Ib. Type la represents the majority of all diamond, and the nitrogen is in the form of platelets. About 0.1% of Type I diamonds are Type lb, in which the nitrogen is dispersed throughout the crystal. Type II: Transparent all the way to 2250 Å; this type contains aluminum. Type IIa does not phosphoresce in SW and contains little nitrogen. Type lIb has bluish phosphorescence in SW and is also electrically conductive. Nitrogen in these diamonds is absent or very scarce.|
|Luminescence Type||Fluorescent, Phosphorescent, UV-Long, UV-Short|
|Enhancements||Some colors produced by irridation, common. Laser drilled to remove inclusions, common. Cracks filled with glass, occassional.|
|Typical Treatments||Fracture/Cavity Filling, High Pressure High Temp (HPHT), Infusion/Impregnation, Irradiation, Laser Drilling, Surface Coating|
|Special Care Instructions||None|
|Transparency||Transparent to opaque.|
|Absorption Spectrum||The absorption spectra of various colored diamonds are quite distinctive and useful, especially in distinguishing irradiation-colored diamond from natural colored stones. The colored diamonds can be grouped into several series: Cape Series: Colorless to yellow diamonds that fluoresce blue. Strong lines at 4155, 4785, 4650, 4520, 4350, and 4230. Most lines are hard to see. Brown Series: Brown, green, and greenish yellow diamonds that fluoresce green. Strong line at 5040 plus weak lines at 5320 and 4980. Yellow Series: Colorless, brownish yellow or yellow and yellow-fluorescing. This series includes the true "canary" yellow diamonds. No discrete spectrum but sometimes a weak line at 4155. Type Il-B Blue: No absorption spectrum. Pink diamonds show the so-called "cape'' absorption line at 4150 and a broad, diffuse band centered at 5500. The strength of this band correlates with the intensity of color of the diamond.|
|Formula||C (carbon ). Essentially pure with only minor traces of impurities.|
|Optics||Isotropic, index very constant; N= 2.417.|
Please also see our detailed article on choosing a diamond and grading diamonds.
Isotropic, index very constant; N= 2.417.
Diamond crystals frequently contain crystals of other minerals.
Diamond is a mineral formed at very high temperatures and pressures, deep within the earth. Synthetic diamond is produced at pressures as high as 100,000 atmospheres (equivalent to 200 miles of rock!) and temperatures around 5000°C; these conditions may approximate those of natural diamond formation. Diamond formed at depth is apparently “exploded” to the surface in fissures that become circular near the surface and are known as “pipes.” The mineralogy of the rocks in these pipes, known as kimberlite, is unusual and unique and reflects high pressure of formation. Diamond is found in kimberlites and also in alluvial deposits (streams, river channels, beaches, deltas, and former stream beds) derived from kimberlite weathering and erosion.
Diamond is the most romanticized and heavily marketed of all gemstones. Nearly every jewelry establishment handles diamonds, even if it has no other gemstones in stock. The annual world production of diamonds is on the order of 10 tons. Of course, only a small percentage of this is gem quality, but diamond of very fine quality is nowhere near as scarce as equivalently high quality ruby or emerald.
From the Greek word adamas, meaning the hardest steel, and hence the hardest gemstone.