DIAMOND

Diamond – C – is a native element of relative rarity, very important as a gemstone and as an industrial mineral. The high price obtained for the diamond in the jewelry store is actually an illusion of value, as the price is manipulated globally by a conglomerate of companies.

The covalent bonds between the carbon atoms of the tetrahedrons of the cubic structure of diamond are responsible for its extraordinary physical properties. Combined with the low levels of contamination (B, N), its high refractive index and transparency, colorless and clear crystals of high brightness are obtained. It has the highest thermal conductivity of all known substances. It is phosphorescent and triboelectric. Its polymorphs are chaoite, graphite and lonsdaleite.

Synthetic diamonds can be produced through two processes. At least 10 other materials (e.g., cubic zirconia) are similar to diamond and used as imitations. There are dozens of techniques to make diamonds more attractive and get higher prices at the jewelry store.

1. Characteristics

Crystal system: Cubic hexaoctahedral.

Color: Yellow, brown or gray to colorless. Rarely blue, green, black, milky, pink, etc.

Habit: Octahedral crystals up to 10 cm, cubic, tetrahedral, dodecahedral.

Cleavage: {111} perfect in 4 directions. Striations: striated and curved faces are common.

Tenacity: Brittle.

Twinning: Contact twins on {111}, penetration twins.

Fracture: Conchoidal.

Mohs Hardness: 10

Parting: No.

Streak: Colorless.

Lustre: Adamantine, resinous.

Diaphaneity: Transparent.

Density (g/cm³): 3.52

2. Geology and Deposits

Diamond formation takes place at depths of 140 to 190 kilometers (up to 300 km?), in the Earth’s mantle, where its growth takes between 1.0 and 3.3 billion years. Diamonds are transported to the surface through deep volcanic eruptions of magma that form kimberlites and lamproites. The primary source of diamonds is therefore formed by the kimberlite rocks contained in volcanic pipes. The weathering of these rocks with the consequent erosion and transport of diamonds forms secondary deposits, which are alluvial deposits (placers) such as gravel and sand, deposited both in a continental environment (river floodplains) and in a coastal environment (ocean beaches). One type of diamond, the “carbonado”, occurring in South America and Africa, may have originated through an asteroid impact 3.0 b.a. ago, but there is no consensus on this origin.

3. Mineral Associations

Diamond occurs with forsterite, phlogopite, diopside, garnet (pyrope), TiO₂ polymorphs (rutile, brookite, anatase), oxides (ilmenite, hematite, magnetite), gold and topaz (placers), among many others.

4. Transmitted Light Microscopy

Refraction indices: n: 2.4354

PLANE POLARIZED LIGHT – PPL

Color / Pleochroism: Colorless.

Relief: Very high.

Cleavage: {111} perfect in 4 directions.

Habits: Octahedral crystals up to 10 cm, cubic, tetrahedral, dodecahedral.

CROSSED POLARIZED LIGHT – XPL

Isotropic.

5. Reflected Light Microscopy

There is no data, nor is it the indicated analytical technique.