Natural Stone Supplies : Material Information : Absolute Black Granite
ABSOLUTE BLACK GRANITE TO THE FUTURE!!! OR SHOULD THAT BE BASALT?
This is not meant to be the definitive guide to absolute black granites, merely an independent and factual assistance to ensure you make the correct specifying or purchasing decision, it may also dispel some of the myths and marketing hype surrounding this material name.
Why? Black is popular, black looks great, black is more expensive, Absolute Black granite has almost become the de facto standard for kitchen tops in some countries, therefore there will always be someone trying to make a quick buck at your expense by selling you an inferior material at the top notch price.
Petrographically, not all black granites are granites, some are basalt, however for generic commercial purposes they are all grouped under the granite name.
Basalts are dark colored, fine-grained extrusive rock. The mineral grains are so fine that they are impossible to distinguish with the naked eye or even a magnifying glass. They are the most widespread of all the igneous rocks. Most basalts are volcanic in origin and were formed by the rapid cooling and hardening of the lava flows. Some basalts are intrusive having cooled inside the Earth's interior.
Terminology
What is meant by "black granite"? To quote from the discussion in ASTM C119-95b Standard we learn the following:
"Black Granites: dark-coloured igneous rocks defined by geologists as basalt, diabase, gabbro, diorite and anorthosite are quarried as building stone, building facings, monuments, and speciality purposes and sold as black granite. The chemical and mineralogical compositions of such rocks are quite different from those of true granites, but black granites nevertheless may be satisfactorily used for some of the same purposes as commercial granite. They possess an interlocking crystalline texture but, unlike granites, they contain little or no quartz or alkali feldspar. Instead, black granites are composed dominantly of intermediate to calcic plagioclase accompanied by one or more common dark rock-forming minerals such as pyroxenes, hornblende, and biotite. Such rocks, because of their relatively high content of iron and magnesium, are designated as ferromagnesian or mafic. An exception is anorthosite which, though commonly dark, consists mostly or entirely of calcic plagioclase". So far a statement by consensus. We can now go ahead to use Black Granite as an umbrella term while offering the material under the (geologically correct) names above.
A more in-depth and technical article written by Asher Shadmon (United Nations' International Commission on Building Stones) may be read here.
To learn more about general rock composition and mineralogy please click here.
Colour
The first common misunderstanding is that of all Absolute Black granites being the same material. They are not and they can vary widely in colour, quality and price!
The original Absolute Black, also known as Sutareboda, is the name for a Swedish black granite which has been quarried for many years.
Probably the most famous Swedish black granite is Ebony Black. It is very hard and durable, takes a beautiful polish and has an almost metallic "ringing" tone when struck with a hammer and chisel. It is also very expensive.
Depending from which quarry it originates it is known as Hallandia AKF No 1, AKF No 25, EGC Black Fined Granied, EGC Black and SS1. We would like to list these correctly therefore please advise if you do know the full details but we do know of the following diabase quarries BRÄNNHULT, DUVHULT, GYLSBODA and HÄGGHULT.
In 1962 Belfast Black granite from South Africa was first exported and shortly afterwards the trade in Italy started calling this granite Nero Assoluto, the literal translation being Black Absolute.
Alternative names have been South African Ebony, South African Black and Prairie. Some of the Southern African granites can actually have a "rice-grained" effect similar to the Canadian Cambrian Black, and the less black qualities also a silver star reflector.
Since the 1960's, Nero Assoluto has become the generic name for many black granites supplied from Italy including Angola, China, India, South Africa, Zimbabwe and many other countries, therefore unless one is specific the granite could actually be from anywhere!
Chinese Black Granites
Great care must be taken when purchasing Chinese black granites since these black granites have become very popular in the last few years owing to their much lower prices, however some of these black granites can be prone to "shakes" and "vents" and many unscrupulous processors/dealers, oil or apply dye to the material to hide these defects.
This would give the granite an effect of fading and correctly polished black granite should not fade! The fading is nothing more than the dyes and oils being removed. Unfortunately the only solution is to re-polish the top and this can be costly.
Before purchasing a granite top perform the following test to find out if it has been doctored. Take a clean white rag and apply some acetone to the surface of the granite. If any residue or black colour is observed on the top, do not accept it, it has been dyed.
The most dense quality Chinese black granite is known as Shanxi Black A Grade and expect to pay as much for this as any top quality Indian black or even more.
Some varieties of Shanxi Black have small gold points in them. Some fabricators do not like this therefore this quality tends to be slightly lower in cost. If you like the gold points and you get a good bargain and the material stands up to the acetone test, well done!
Be very wary if you are offered Shanxi Black B Grade since, not being of an export quality, it is not generally used outside of China owing to its inability to take a good gloss polish.
Indian Black Granites
India first started exporting high quality black granites at the end of the 1960's and by the end of the 70's volume production of memorials and slabs were well under way.
Some of the finest quality, reasonable cost, dense/absolute blacks are the black granites from the south of India however some of these, including the very dense Khammam/Kunnam Black, can be very "soft", therefore care must be taken when specifying these for projects and even kitchen tops since they can scratch and show scuff marks.
In general terms the absolute black granites from the Warrangal area are both dense black in colour and much harder taking a superb polish and wearing well. Others include Dharmapuri and Mettur Districts of Tamil Nadu, Chittoor and Khammam in Andhra Pradesh and Kanakpura near Bangalore, where a variety of medium and light medium black granites are found.
Unlike basalts, many of these granites have a small rice-grain sized crystal structure which can easily be seen with the naked eye however, precisely because of the crystal structure, the colour appearance may not be as dark as a black basalt.
Many purchasers prefer this type of granite since it appears more natural than the compact black basalts which can look like a processed, man-made material. It's the buyer's perogative!
During the past 30 years these black granites have been used more for memorial production than any other black granite therefore the quality and durability speaks for itself.
Indian black granites are known under the names of BG Black, Indian Dense Black, Indian Jet Black, Premium Black, Supreme Black, Indian Super Black, Nero Assoluto Indiano, and probably several others!
Black Galaxy
Black Galaxy is from Ongole in India, the original Galaxy material with the densest black background and bright reflectors, is known as Star Galaxy. The Star Galaxy quarry is not a massive one therefore the volume of blocks produced could not supply all the dealers who purport to sell this material.
The gold specks are due to the presence of ferrous rich Enstatine (Bronzite). Black galaxy can be broadly divided into three types based on the size of the gold coloured specks as 1. Large Specked Black Galaxy, 2. Medium Specked Black Galaxy and 3. Small Specked Black Galaxy Granite.
There are over 40 quarries spread over 400 acres of land. The sizes of quarries range between 2 and 20 acres each. Around 3500 CBM to 4500 CBM of black galaxy granite is produced every month. Only 40% of the volume make up big blocks and are commonly called gang-saw size blocks. These are blocks of sizes above 2.40m x 1.20m x 1.00m.
Black Galaxy is actively traded as a commodity and owing to the large volume of quarrying, large blocks in First Choice material are becoming scarcer and much more expensive. Black Galaxy, like all natural materials, is susceptible to variations in veining, however it must be stressed that the possibility of one or two lines may probably occur in large slabs.
It is very important to view Black Galaxy before buying and not to buy on price alone.
There are many other countries quarrying black granites including Brazil, Canada, Finland, Iran, Namibia, Spain, Transkei, Ukraine and the USA.
Some granites are sold under a black name such as Nero Impala from South Africa, APP Black from India and G654, aka Padang Dark & Sesame Black from China however, because of their colour structure, they are generally considered to be dark greys rather than a black.
Having said that they are some of the most popular black/dark granites in the world and have been used on some of the most prestigious projects and domestic environments therefore to dismiss them would be ridiculous.
It is quite possible that your dealer/fabricator may be unaware of much of the above, therefore it would be wise to discuss your black granite purchase with several suppliers before making your specifying decision just to ascertain how much they really do know, or whether they are simply trying to fob you off with a sub-standard material at premium quality prices.
As always "Caveat Emptor - Buyer Beware!"