From a petrographic view not all of the black coloured granite are actually granites, some of them (depend of the mineral composition) can be basalt, diorite, gabbro, granodiorite. Important thing about commercial granite is that, whatever its actual mineral composition, it is suitable for hard use.
Any dark colour granite takes a good polish and resists scratches, acids and it have an attractive colour pattern.
A good reason to choose black granite for a worktop is the rich and elegant appearance. The very popular Absolute Black granite, which has been quarried in Sweden for many years, is most likely the original of this type and its very expensive.
From 1962 South Africa began to export Belfast Black granite and stone providers from Italy started calling this granite Nero Abssoluto meaning black absolute.
Alternative names for black South African granite are South Africa Ebony, South African Black and Prairie. Some of the South African granites can be “salt and pepper” in appearance and some can contain less black and more silver pits.
Few years ago black granite has entered on the market from China at lower prices. Some of this is a good quality, but caution is advised as some of these black granites can have vents and pits and some dealers apply oil or dye to the slabs to hide these defects.
In time this type of black granite will fade in colour and it will look slightly grey. This can be remedied but unfortunately the only solution it to re-polish the top and this can be very expensive.
There is a test you can carry out to see if the black granite has been heavily died. You take a clean cloth, add a little acetone and gently wipe on the granite. If the cloth brings off some of the colour then you know it has been died.
The most dense black granite from China is known as Shanxi Black A Grade and believe it or not you can expect to pay as much for this granite as any top quality black, sometimes more. Since 1960 Nero Abssoluto is a common name for most of black granite supplied from Italy, Angola, China, India, South Africa, Zimbabwe and many other countries. This means your black granite could actually be from anywhere!
Few facts about black granite The Mohs Scale is used to determine the relative hardness of a mineral as a comparison to another mineral. Because granite is a rock composed of multiple minerals, only crystals of specific minerals within the granite would be tested for hardness.
Granite is typically composed of quartz (Mohs-7), potassium feldspar (Mohs-6), and biotite and muscovite micas (Mohs-2.0-2.5).
As the result of pressure and heat in the forming process, inside the rocks like granite and basalt, very small pores can appear. Anyhow, in the cooling process stone particle can contract by over 40% causing fractures. In consequence rocks such as granite or diorite are classified as having fractures more than a pores.Porosity of the granite can vary from 0.4% to 1.5%
Black Granite is a very dense stone and do not need to be sealed but this problem will be discussed more in near future.
I hope this informations will bring you one step closer to your decision what stone you should use for your new kitchen and you can contact us for any other question regarding granite, marble or quartz worktops
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