Stones guide
I. Some concepts
Sparkle (or refractive index)
Small reminder of our physics classes. The refractive index (n) of an area is the ration of the speed of light in a vacuum and of this same speed in that area (v). n=c/v. Thus, the refractive index of the air is 1.
Of this concept, we can deduce that the amount of light reflected from the crown of a stone (for example, diamond) towards our eye (the sparkle) depends on the refractive index. It is obvious that the greater is the amount of light reflected, the brighter is the stone. We can increase the amount of light reflected by size. Thus, the stones with high refractive indexs, such as diamond etc, are usually carved to increase their shine. That means the pavilion facets must be cut with correct angles so that the light can be reflected on the crown instead of going by the gem breech. Normal, the bottom of the gem being set in the jewel, there is no use for the light to reflect there.
Dispersal (or Fire)
The refractive index of an area depends on the wavelength of the light that goes through it. It is a bit weaker when the lights of wavelength are high.
Thus, various wavelengths refract differently. For example, a purple light is more refracted than a red one. But the lights around us (lamp, daylight etc) are polychromatic. So the various light spectrum are refracted in slightly different directions. See it as a prism, when a polychromatic light goes through it, we have a rainbow. When a polychromatic light goes through a carved stone, it's exactly the same thing. "The fire" of a gemstone is its tendency to separate light into its spectral colours. The fire is one of the features of the stones that have a high refractive index, like first and foremost, diamond. The more transparent is the diamond, the more important is the light scattering effect.
Look what we obtain.
Sheen (or reflection from the surface)
When light arrives over the surface of a stone, some rays are reflected while some others enter the stone and are instead refracted. The reflected light is called "first-surface reflection" or sheen.
Solidity and Mohs' scale
A stone strength is determined by its resistance to scratches, its solidity. To identify it, gemmologists refer to the Mohs' scale. It consists in a list of 10 easily found minerals, numbered from de to 10. In order to identify the strength of a mineral, we compare it to another one whose solidity is already known.
1. Talc, friable under the nail
2. Gypsum, scratchable with the nail
3. Calcite, scratchable with a copper coin
4 . Fluorine, scratchable (easily) with a knife
5. Apatite, scratchable with a knife
6. Orthoclase, scratchable with a lime or sand
8. Topaz, scratchable with tungsten carbide
II. The stones
Amethyst
Name origin : the word “amethyst” is derived from the greek word “methystos” that means “drunkenness”. "amethyst" would then mean "who is not drunk"
Family : quartz
Composition : silicium dioxide
Solidity : 7
Densitéy: 2,65
Crystalline system : trigonal
Colours : varying from pale to deep purple
Sparkle : glassy
The amethyst is a purple quartz. It is of magmatic origin. Just like all quartz, it is composed of silicium dioxide. Its solidity is of 7 on the Mohs' scale and its density turns around 2,6. In its raw form, this stone varies between a violaceous and purple hue. The colour is due to the iron impurities that we can find in its crystalline. When you heat an amethyst up, its colour stays stable up to 250°. From 500 °C, it becomes light yellow. It is quite common for amethysts to be heated up to high temperature in order to modify, intensify and fix their colours .
Virtues : The amethyst is a powerful medicine against any kind of emotional negativity. It is considered as the humility stone and the wisdom stone. It boosts creativity, imagination and clarity of mind.
Citrine
Name origin : colour of lemon
Family : quartz
Composition : silicium dioxide
Solidity : 7
Density : 2,65
Crystalline system : trigonal
Colours : yellow-orange
Sparkle : glassy
The citrine is a quartz and is composed of iron and silicium oxide. We sometimes call it "Yellow hyaline quartz”. Its yellow colour is due to the low presence of iron oxide.
Beware not to be scammed. Heated up amethysts over 500°C are often sold as citrines;
Virtues : Citrines attract success, but also protect from fears, blockages, and harmful people that could make your optimism go to waste. They favour the balance of energies as well as concentration. They are energizing and strongly develop creativity.
Cubic zirconia, zirconia & zircon
Zirconia (or zirconium) is a ziconium dioxide or oxide. It is made in laboratory. Don't mistake it for zircon, zirconium silicate found at raw state whose transparent specimens are used in the jewellery industry to replace diamond. Zircons posses a colour varying from yellow to garnet.
Zirconia, however, is a lab, a stone created in laboratory following a chemical formula. It is an opaque ceramic. It is used in the fabrication of some watches and for ceramic knives etc. It allows almost unscratchable watches. It is called cubic zirconia when transparent. It then replaces perfectly diamond. In laboratory, we easily give it all kind of colours. Considering its high refractive index, it is very used in the jewellery industry. One problem : its solidity makes its polish hard. In the Vicker's scale mod, zirconia has a solidity of 1200 hv. It is located between quartz (1100 hv and 7 on the Mohs' scale) and topaz (1400 hv and 8 on the Mohs' scale)
Zircon
Cubic zirconia
Emerald
Name origin : the word "emerald" would come from the latin word "smaragdus", deformation of the persian word "zamarat" that means « heart of stone ».
Family : silicate
Variety of beryl
Composition : aluminium and beryllium silicate
Solidity : Between 7,5 and 8
Density : 2,7 - 2,9
Crystalline system : hexagonal
Colours : green-blue, deep lime green, light and dark.
Sparkle : glassy
From the silicates family, the emerald is a variety of beryl. The chromium, vanadium and iron contained in the emerald give it its green colour. When submitted to fire, the emerald takes a light green hue. This stone possesses a solidity between 7,5 and 8 on the Mohs' scale.
Virtues : provides harmonious relations, heals claustrophobic disorder up, facilitates learning and sharpens memory, strenghtens the immunity system. This stone, that allows a better recovery of physical capacities, is recommended to convalescing people.
Garnet
Name origin : garnet comes from the latin name " malum granatum" (grain apple, grenade), for its colour and of "granum" (grain) for its shape.
Family : garnet
Composition : aluminium and iron silicate
Solidity : Between 6,5 and 7,5.
Density : 3,5-4,3
Crystalline system : cubic
Colours : Red, Brown, sometimes violaceaous..
Sparkle : glassy to resinous
Formerly called anthrax (coal), garnets have been used in the jewellery industry for millennias.
They are part of the mesosilicate group. Lots of chemicals elements make them up. As a result, garnets have varied colours.
Some garnets are starred. They have acicular and parallel inclusions. Those inclusions allow a refraction of light that gives a star-like effect.
Virtues : garnet brings faith and strength to live, energy, courage, driving force and assurance. We associate the power of will, a better self-confidence and success to it.
Jade
Name origin : the word "jade" comes from the spanish "piedra de ijada", stone for the pit.
Family : Augites
Composition : aluminium and sodium double silicate
Solidity : Between 6,5 and 7
Density : 3,34
Crystalline system : monoclinic
Colours : variable.
The word "jade" designate 2 minerals :
- the nephrite jade, essentially composed of nephrite, magnesium and calcium silicate. That kind is quite common.
- the jadeite jade, essentially composed of jadeite, aluminium and sodium silicate. It is more solid, dense and rare.
Usually, the jade is of green colour, more or less darkened. We can find some white-coloured. When it is made up of cobalt salts, it is of green-blue colour and of black colour when composed of titanium salt. It is also possible to find some pink-coloured when it is composed of manganese and iron salts.
Virtues : The jade helps find inner peace, cross difficult events and heals emotional injuries. It helps find back a positive state of mind.
Moissanite
Name origin : Henri Moissan
Family : silicate
Composition : carbon and silicium
Solidity : 9,5
Colours : colourless, green, yellow
Essentially labs
Moissanite or silicium carbide (SIC) was discovered in 1904 by Henri Moissan in the meteorite of Canyon Diablo in Arizona. Considering its rarity, we recreate it in laboratory.
This stone can compete with diamond. It has a refractive index of 2.55 against 2.42 for the diamond and 2.12 for the zirconia. It has a solidty of 9,5 on the Mohs' scale but can sometimes cratch the diamond, which has 10 on that scale.
The moissanite has heat-resistant properties superior to that of lots of other stones, what allows for an easier repairing of jewels. It withstands very high temperatures without being altered.
The density of the moissanite (3,21) is slightly inferior to that of the diamond (3,52). As a result, the caratage linked to the stones dimension must be adapted. We then talk about "Diamond Equivalent Weight" (DEW).
Opal
Name origin : comes from the sanskrit word "upala" that means " gemstone". "Upala" gives the greek word "opallion" and the latin word "opalus" = "to see a change of colours".
Family : silicate
Composition : dioxyde de silicium hydreux
Solidity : Between 5.5 and 6.5
Colours : various
Sparkle : glassy, resinous, pearly, waxy, greasy, mat.
An opal is a mineral composed of hydrated silica. We can find uranium, magnesium, calcium, aluminium, iron, arsenic, sodium and potassium in it. The opal can contain fossilized organisms.
Virtues : the opal contributes to the awakening of consciousness, helps to let go and live the present time.
Peridot
Name origin : ???
Family : Olivine
Composition : ferrous magnesium silicate
Solidity : Between 6.5 and 7
Density : 3,32 à 3,37
Crystalline system : Orthorhombic
Colour : green
Sparkle : glassy to greasy
Like diamond, the peridot is created deeply into the Earth's mantle. It's the tectonic plates movement and the volcanic action that reject those stones to the surface. Peridot contains magnesium, iron and silica. It owes its formidable green to the nickel or chromium that it contains.
Its colour looks like that of the emerald. That explains why it is often called "emerald of the poor".
Virtues : the peridot acts mentally over the person to improve their self-confidence and reduce stress to make way to a mental toughness.
Pink quartz
Name origin : the name "pink quartz" comes from the word “quaterz”, meaning “bad mineral”.
Family : silicates
Composition : silicium dioxide
Solidity : 7
Density : 2,65
Crystalline system : trigonal
Colours : pink
Sparkle : glassy, white
Pink quartz is a variety of quartz coloured with metallic oxides, manganese, titanium. Just like other quartz, pink quartz is to be found in large crystals, pink and translucent.
Virtues : Since always, pink quartz maintains a relationship with love and heart. It's a stone of peace, love and friendship.
Ruby
Name origin : the word "ruby" comes from the latin "ruber" which has given "red".
Family : corundum
Composition : aluminium oxide
Solidity : 9
Density : 3,97 - 4,05
Crystalline system : trigonal
Colours : red, with brown and purple variations
Sparkle : glassy, greasy, mat
Ruby is the red version of corundum, the blue one being the sapphire. It's a very rare mineral. It can be of magmatic origin or be the result of the modification of preexisting rocks under the effect of warmth and strong presssures. To make a ruby take form, you need aluminium, silica, and a little bit of chromium for the colour.
Virtues : the ruby will help you recover joy and passion, while stimulating your creativity and bringing wisdom daily.
Sapphire
Name origin : ???
Family : corundum
Composition : aluminium oxide
Solidity : 9
Density : 3,95 - 4,03
Crystalline system : trigonal
Colours : pale blue, night blue, with possible violaceous shades, yellow, orange or colourless, and more rarily, black, purple, green and pink.
Sparkle : glassy
Sapphire is a variety of corundum that exists in various colours. It consists of aluminium oxide crystals that contains impurities, giving it different variations of colours (titanium and iron for blue, vanadium for purple, chromium for pink, steel for yellow and green.) We can heat the sapphire up in order to act on its colour. This proccess allows to heighten colour and clarity by dissolving the traces elements in the stone.
Virtues : favouring inspiration, spiritual elevation and meditation
Tanzanite
Name origin : its name comes from Tanzania, country where this stone was discovered.
Family : zoïsite, subgroup of the silicates
Composition : aluminium and calcium silicate
Solidity : 6,5
Density : 3,15 - 3,37
Crystalline system : orthorhombique
Colours : blue, violaceous blue, bluish purple
Sparkle : pearly, glassy
The tanzanite is a blue to purple variety of zoïsite discovered in Tanzania. Its colours, varying from azure to purple, are due to the presence of chromium andvanadium. For the deep blue colour, it comes from the exposure to high temperatures that result from the volcanic action of the Kilimanjaro
Most tanzanites from the market have passed heat threatment to obtain or maintain their colours.
Virtues : the tanzanite is associated with creativity and imagination, what makes it the best ally of artists.
Topaze
Name origin : unclear origin. from sanskrit "tupas" that means"fire" or from the island of Topazos in the Red sea
Family : nesosubsilicate
Composition : aluminium fluosilicate
Solidity : 8
Density : From 3,49 to 3,57
Crystalline system : orthorhombic
Colours : colourless to white, blue, greenish, brown-yellow, orange, pink, reddish, purple, brown.
Sparkle : glassy
Topaze is a mineral specie from the silicates group, subgroup of the nesosubsilicates that can contain traces of iron, chromium, magnesium and titanium. The topaze is declined in various colours : yellow, blue, pink, white, red, purple, green and even colourless. the topaze pigmentation can be changed by effect of a treatment : diffusion of ions over the surface of the crystal or irradiations. It is also possible to change the colour by heating the topaze up or using the coating method.
Virtues : very polyvalent, the topaze energizes the body and appeases the mind.
Tourmaline
Name origin : comes from the singhalese "thoramali" or "thuramali"
Family : Tourmaline
Composition : complex silicate of aluminium borosilicate with iron, magnesium and alkalis
Solidity : Between 7 and 7,5
Density : From 2,90 to 3,25
Crystalline system : trigonal
Colours : various
Sparkle : glassy
The tourmaline is a common mineral from magmatic and metamorphic rocks, as well as hydrothermal veins of high temperature. The pink hue of tourmalines with various deposits is the result of a continuous natural due to the manganese.
Virtues : it possesses the ability to absorb all positive vibrations.
