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diamond

THE MINERAL DIAMOND

• Chemistry: C, Elemental Carbon
• Class: Native Elements
• Subclass: Non-metallics
• Group: Carbon
• Uses: usually as a gemstone and abrasive, also scientific uses.

Diamond is the ultimate gemstone, having few weaknesses and many strengths. It is well known that Diamond is the hardest substance found in nature, but few people realize that Diamond is four times harder than the next hardest natural mineral, corundum (sapphire and ruby). But even as hard as it is, it is not impervious. Diamond has four directions of cleavage, meaning that if it receives a sharp blow in one of these directions it will cleave, or split. A skilled diamond setter and/or jeweler will prevent any of these directions from being in a position to be struck while mounted in a jewelry piece.

As a gemstone, Diamond's single flaw (perfect cleavage) is far outdistanced by the sum of its positive qualities. It has a broad color range, high refraction, high dispersion or fire, very low reactivity to chemicals, rarity, and of course, extreme hardness and durability. Diamond is the April Birthstone.

In terms of it's physical properties, diamond is the ultimate mineral in several ways:

• Hardness: Diamond is a perfect "10", defining the top of the hardness scale, and by absolute measures four times harder than sapphire (which is #9 on that scale).
• Clarity: Diamond is transparent over a larger range of wavelengths (from the ultraviolet into the far infrared) than is any other solid or liquid substance - nothing else even comes close.
• Thermal Conductivity: Diamond conducts heat better than anything - five times better than the second best element, Silver!
• Melting Point: Diamond has the highest melting point (3820 degrees Kelvin)
• Lattice Density: The atoms of Diamond are packed closer together than are the atoms of any other substance
• Tensile Strength: Diamond has the highest tensile strength of any material, at 2.8 gigapascals. However, that does not quite translate into the strongest rope or cable, as diamond has cleavage planes which support crack propagation. The strongest ropes can likely be made from another material, carbon nanotubes, as they should not suffer from the effects of cracks and break. Still, if a long, thin, perfect crystal of diamond could be manufactured, it would offer the highest possible pulling strength (in a straight line - don't try to tie it in a knot!)
• Compressive Strength: Diamond was once thought to be the material most resistant to compression (the least compressible). It is the material that scientists use to create the greatest pressures when testing matter. However, the rare metal Osmium has recently been shown to be even less compressible (although it is not as hard as diamond). Diamond has a bulk modulus (reciprocal of compressibility) of 443 GigaPascals (GPa). The bulk modulus of the metal osmium has recently been found to be 476 GPa, about 7% greater than diamond.

Diamond is a polymorph of the element carbon. Graphite is another polymorph. The two share the same chemistry, carbon, but have very different structures and properties. Diamond is hard, Graphite is soft (the "lead" of a pencil). Diamond is an excellent electrical insulator, Graphite is a good conductor of electricity. Diamond is the ultimate abrasive, Graphite is a very good lubricant. Diamond is transparent, Graphite is opaque. Diamond crystallizes in the Isometric system and graphite crystallizes in the hexagonal system. Somewhat of a surprise is that at surface temperatures and pressures, Graphite is the stable form of carbon. In fact, all diamonds at or near the surface of the Earth are currently undergoing a transformation into Graphite. This reaction, fortunately, is extremely slow.

http://www.galleries.com/minerals/elements/diamond/diamond.htm

Rutile

THE MINERAL RUTILE

• Chemistry: TiO2, Titanium Oxide
• Class: Oxides and Hydroxides
• Group: Rutile
• Uses: Ore of titanium, pigment and as an ornamental stone when in clear quartz

Rutile is an interesting, varied and important mineral. Rutile is a major ore of titanium, a metal used for high tech alloys because of its light weight, high strength and resistance to corrosion. Rutile is also unwittingly of major importance to the gemstone markets. It also forms its own interesting and beautiful mineral specimens.

Microscopic inclusions of rutile in quartz, tourmaline, ruby, sapphire and other gemstones, produces light effects such as cat's eye and asterisms (stars). A beautiful stone produced by large inclusions of golden rutile needles in clear quartz is called rutilated quartz. Rutilated quartz is sometimes used as a semi-precious stone and/or for carvings. This stone is produced because at high temperatures and pressure, n(SiO2)-n(TiO2) is in a stable state but as temperatures cool and pressure eases the two separate with rutile crystals trapped inside the quartz crystals.

Twinning is common in rutile crystals, with a cyclic twin forming that is comprised of six or even eight "twins" arranged in a circle. A Rutile Star is a formation of crystals of rutile in a six rayed orientation. The crystals grow off of a hematite crystal and the orientation is caused by its six rhombic faces.

physical characreristic

• Color is black or reddish brown in large thick crystals or golden yellow or rusty yellow as inclusions or in thin crystals.
• Luster is adamantine to submetallic.
• Transparency: Crystals are transparent in rather thin crystals otherwise opaque.
• Crystal System is tetragonal; 4/m 2/m 2/m
• Crystal Habits include eight sided prisms and blocky crystals terminated by a blunt four sided or complex pyramid. The prisms are composed of two four sided prisms with one of the prisms being dominant. Crystals with some twins forming hexagonal or octahedral circles. A very common habit is thin acicular needles (especially as inclusions in other minerals) or as blades.
• Cleavage is good in two directions forming prisms, poor in a third (basal).
• Fracture is conchoidal to uneven.
• Hardness is 6 - 6.5
• Specific Gravity is 4.2+ (slightly heavy)
• Streak is brown
• Other Characteristics: Striations lengthwise on crystals, high refractive index (2.63) gives it a sparkle greater than diamond (2.42).
• Associated Minerals are quartz, tourmaline, barite, hematite and other oxidessilicates. and
• Notable Occurrences include Minas Gerias, Brazil; Swiss Alps; Arkansas, USA and some African locallities.
• Best Field Indicators are crystal habit, streak, hardness, color and high index of refraction (luster).

http://www.galleries.com/Minerals/Oxides/RUTILE/RUTILE.htm