Diamond’s cleavage produces step-like breaks like the one seen near the girdle of the round brilliant; a piece of glass shows the smooth, curved fracture surface typical of simulants.
As is the case with most gem materials, diamond has various physical and optical properties which can be measured very precisely by a trained person with the right equipment. Here are some of its important identifying properties and characteristics:
- Refractive index (RI): 2.417
- Dispersion: .044
- Luster: adamantine
- Transparency: exceptional
- Specific Gravity (SG): 3.52
- Hardness: 10 on Mohs scale
- Toughness: good in cleavage directions; otherwise exceptional
- Cleavage: four directions, perfect
- Fracture: step-like (alternating straight cleavages and conchoidal fractures)
- Included crystals: angular ones are unique in type and appearance
- Polish: superior (best possible)
- Facet edges: sharp (typically)
- Girdle: normally waxy to granular; bearding common
- Naturals: show characteristic growth markings
- Spectra: positive identifying absorption lines at 592, 504, 498, 478, 456, and 415 nm
- Wetability: difficult
- Thermal inertia: highest of any substance
- Response to X-rays: transparent; almost always fluoresces blue
General Characteristics of Simulants
Although you can normally separate any diamond simulant from diamond simply and reliably with the diamond thermal tester, there are a number of other characteristics that expose various simulants for what they are. Here are some of the more obvious ones:
- All common diamond simulants (except some glass and some doublets) have higher SGs than diamond.
- Only synthetic rutile, strontium titanate, and CZ have significantly higher dispersion than diamond.
- Man-made stones may contain gas bubbles.
- Like diamonds, many common simulants do not give a reading on standard refractometers (over the limits); but synthetic sapphire, synthetic spinel, most glass, and some doublets do.
- Synthetic rutile, zircon, and synthetic sapphire are doubly refractive; diamond is singly refractive.
- Simulants with RIs below that of strontium titanate can have a read-through effect.