About gemstones

Tanzanite

Tanzanite is a trade name given to Blue Zoisite. The name was chosen because the world only known deposit of Tanzanite is in Northern Tanzania at the foot of Mt Kilimanjaro in Mererani hills.

Zoisite mineral naturally occurs in green, red, pink, yellow, blue, and purple minerals.

The laboratory discovery of heat treatment on brown and green zoisite made the blue zoisite readily available for the vast market. Only about 5% of the mined Tanzanite is found in naturally blue dominant hue.

The blue colour in Tanzanite is caused by the presence of vanadium mineral which enhances brilliantly when heated to 600 degrees Celsius for 30mins.

Today almost all the blue Tanzanite sold in the market has been heat treated.

Tanzanite has pleochroic properties. pleochroism is a physical property of a mineral that allows it to display a different colour from every different angle it is viewed. Tanzanite is a Trichroic because it displays 3different colours when viewed from three different sides of its crystal. 

Tanzanite has Mohs hardness of 6.5 and gravity of 3.35.

The colour sustainability of Tanzanite is good with heat treated gems holding their colour timelessly. Like most gems, Tanzanite is likely to be damaged by acid. It is sensitive to rapid change of temperature and might break. Tanzanite might also chip or break subject to pressure, due to its one directional cleavage.

Tourmaline

is a crystalline boron silicate mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. This gemstone can be found in a wide variety of colours.

Tourmaline is not a single mineral, but a group of several closely related minerals. The three most well-known members are Elbaite and Dravite. Elbaite offers a wide range of gem quality tourmaline colours. Other lesser-known members include Uvite, Liddicoatite and Buergerite. Tourmaline is extremely varied in colour. Colours include black, brown, green, red, pink, blue, and grey. White, colourless, yellow, orange, and purple colours are less common. Crystals are frequently multi-coloured, containing two or more distinct colours. 

Many tourmaline colour varieties have inspired their own trade names:

Rubellite is a name for pink, red, purplish red, orange red, or brownish red tourmaline, although some in the trade argue that the term shouldn’t apply to pink tourmaline.

Indicolite is dark violet-blue, blue, or greenish blue tourmaline.

Paraiba is an intense violet-blue, greenish blue, or blue tourmaline from the state of Paraiba, Brazil.

Chrome tourmaline is intense green. In spite of its name, it’s coloured mostly by vanadium, the same element that colours many Brazilian and African emeralds.

Parti-coloured tourmaline displays more than one colour. One of the most common combinations is green and pink, but many others are possible.

Watermelon tourmaline is pink in the centre and green around the outside. Crystals of this material are typically cut in slices to display this special arrangement.

Hardness 7-7.5, Transparent to opaque, Specific gravity 2.9-3.3.

Sapphire

Very precious and valuable. It is a very desirable gemstone due to its excellent colour, hardness, durability, and lustre. In the gem trade, Sapphire without any colour prefix refers to the blue variety of the mineral corundum. However, Sapphire comes in a variety of colours I.e.: White, Colourless, Blue, Green, Yellow, Orange, Brown, Pink, Purple, Gray, Black, Multi-coloured. The red Corundum carries its own name which is ruby (the red variety of Corundum) which has its own name since antiquity.

Ruby

A ruby is a pink to blood-red coloured gemstone, a variety of the mineral corundum (aluminium oxide). Ruby is one of the traditional cardinal gems, together with amethyst, sapphire, emerald, and diamond. The word ruby comes from rubber, Latin for red. The colour of a ruby is due to the element chromium. 

The quality of a ruby is determined by its colour, cut, and clarity, which, along with carat weight, affect its value. 

Sapphire/corundum has a hardness of 9

Important Sapphire sources include Burma (Myanmar), Sri Lanka, Thailand, Cambodia, Madagascar, Tanzania, Australia, and the U.S. (Montana). The Kashmir region of India/Pakistan was famous for its Kashmir-blue Sapphire, but little material comes from there.

Emerald

Emerald is a gemstone and a variety of the mineral beryl coloured green by trace amounts of chromium and/or sometimes vanadium. Beryl has a hardness of 7.5–8 on the Mohs scale.

The colour of Emerald is green. The light green form of Beryl is not recognized as Emerald, but rather green beryl. The deep colour of 

Emerald is caused by traces of chromium, but sometimes also vanadium.

Most emeralds are highly included, so their toughness (resistance to breakage) is classified as generally poor. Emerald is a cyclosilicate.

Beryl

It is an allochromatic meaning it is colourless in its purest form. Its varieties are Aquamarine, Golden beryl, Goshenite, Green beryl and Emerald. The varieties of Beryl are coloured by traces of metallic elements. Aquamarine (sea green to sky blue hue is caused by traces of Iron, Golden, yellow, and greenish beryl also known as heliodor also coloured by the presence of iron minerals while Emerald is coloured by the presence of chrome and vanadium. Sources of Beryl are Zimbabwe, Zambia, Namibia, Muzo in South America, Tanzania, Afghanistan, Madagascar, Mozambique, etc.

Green Beryl

The pale green variety of beryl is not referred to as emerald, but simply as green beryl or aquamarine. “Green beryl” is the name given to light green specimens of beryl that don’t have a tone and saturation dark enough to merit the name “emerald.” a number of this light green beryl is coloured by iron and does not have a the distinct colour or saturation to merit it as Emerald.

Morganite

Morganite is the pink to orange-pink variety of beryl, a mineral that includes emerald and aquamarine. Blends of pink and orange are typical natural morganite colours

Subtle colour comes from traces of manganese. Morganite typically ranges from pink to orange pink in colour, but these colours are very subtle in naturally occurring stones. Mineral type is beryl, lurers are pink to orange pink. Refractive index: 1.583 to 1.590, Mohs hardness is 7.5 to 8.

Aquamarine

Aquamarine is the name for gem-quality mineral Beryl that are within a colour range of greenish blue to blue. The name is used regardless of a stone’s hue tone or saturation. Pure beryl is colourless. Most aquamarine has a very light colour, which can be almost unnoticeable in very small stones. Stones with a rich blue colour are the most popular. They are also the rarest and most valuable. 

Aquamarine is one among the harder gemstones with Moh’s hardness of 7.5 to 8. The greenish blue to blue colour of aquamarine is caused by trace amounts of iron that is Ferrous iron (Fe²⁺); and ferric iron (Fe³⁺) is responsible for yellow colour (which combines with the blue colour to produce greenish blue).  Aquamarine/Beryl is found there in both pegmatites and alluvial deposits. 

Sources of aquamarine are: Afghanistan, Kenya, Madagascar, Malawi, Mozambique, Nigeria, Pakitan, Russia, Tanzania, Zambia,India, Sri Lanka and in the United States.

Garnets 

Garnets are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms but differ in chemical composition. The different species are pyrope, almandine, spessartine, grossular, uvarovite and andradite. The garnets make up two solid solution series: pyrope-almandine-spessartine and uvarovite-grossular-andradite.

Mohs scale hardness: 6.5–7.5
All species of garnets possess similar physical properties and crystal forms but differ in chemical composition. The different species are pyrope, almandine, spessartine, grossular (varieties of which are hessonite or cinnamon-stone and tsavorite), uvarovite and andradite. The garnets make up two solid solution series: pyrope-almandine-spessartine (pyralspite) and uvarovite-grossular-andradite (ugrandite).

Tsavolite / Tsavorite

The other green garnet, known as Tsavorite is quite different. Demantoid is from the andradite family of garnets, tsavorite is a variety of grossular from the ugrandite family of garnets. Demantoid has more dispersion than tsavorite and tends to be more of a grassy/yellow green. Tsavorite can be found in an emerald, green colour.

Though Tsavorite is found in both Tanzania and Kenya, the very finest Tsavorite, with the purest green hues is still only found in Tsavo, Kenya. The Kenya-Tanzania border, an area of raw beautiful African wilderness has a history of violent volcanic activity and due to these volatile geological conditions under which it forms, Tsavorite is only found in relatively small sizes. Stones over 2.5 carats are considered very rare and valuable. 

Rhodolites

Rhodolite describes a rose-red form of garnet that has a lighter tone and more purplish colour than typical Garnet gemstones. It is often regarded as a variety of pyrope.

Rhodolite has a hardness of 7-7.5 Mohs scale N=1.750-1.760 (Zimbabwe); 1.760-1.761 (North Carolina); 1.745-1.760 (Tanzania).

Spessatite / Orange Garnet

Spessartite garnet is an orange to red-brown gemstone that belongs to the large and varied garnet species of gems. The garnet group can be classified into two primary classes: pyrospites (aluminium) and ugrandites (calcium) garnets. It has a chemical composition of Manganese aluminium silicate

Colour: Orange, orangey-yellow, red brown

Hardness: 6.5 to 7.5 on the Mohs scale

This form of Garnet was once much rarer, but new abundant finds in Tanzania, China, and Pakistan have really put Spessartine on the map, making it very well regarded spessartite has a hardness of 7 Mohs scale