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Granite Information

Absolute Black & Star Galaxy

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.
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.

Chinese 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.
Great care must be taken when purchasing Chinese black granites. The most dense quality Chinese black granite is known as Shanxi Black and expect to pay as much for this as any top quality Indian black.
Some varieties of Shanxi Black have small gold points in them. Some fabricators do not like this therefore this quality tends to be lower in cost.

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.
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.
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.

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 from China however, because of their colour structure, they are generally considered to be dark greys rather than a black.

Learning more about Granite

Granite is a very hard, crystalline, igneous rock primarily composed of feldspar, quartz, orthoclase or microcline accompanied by one or more dark minerals. It is visibly homogeneous in texture. It is the most common plutonic rock of the Earth's crust, forming by the cooling of magma (silicate melt) at depth.
The term "Granite" is derived from the Latin word "Granum" meaning "grain" because of its granular nature. Italian granito, from past participle of granire to granulate, to make grainy, from grano, grain.
Granite is the hardest building stone and occupies a prominent place among dimensional stones on account of its hardness, resistance to weathering, capability to take mirror polish, fascinating colours and textural patterns.
The principal characteristics of dimensional granite also include high load bearing capacity, crushing strength, abrasive strength, amenability to cutting and shaping without secondary flaws, ability to yield thin and large slabs and - above all - durability. Due to its dense grain it is impervious to stain. Polished granite slabs and tiles have achieved a special status as building stones world over.
Granite is used as a building material in the form of granite tiles and granite slabs for wall cladding, roofing and flooring and a variety of other interior and exterior applications and especially for counter tops, kitchen work tops and vanity units and is the most popular material for monuments and memorials.

Granite Myths

Not all granites are "true" granites however for commercial purposes they are grouped together.
Not all black granites are the same. Learn more here.
Granite will scratch and chip when abused however it can be repaired!
Granite can stain however it is possible for it to be removed.
Not all granites need to be sealed.
If a granite needs to be sealed, do it since this will avoid most problems.
Sealing correctly is not a five minute job. Take care and time and do it properly.
Granite sealed correctly will last for many years before "topping up".
Granite does not contain harmful radon gases.
Granite does not come from only mountainous regions.
Thin and long narrow lengths of granite will break easily.
If the granite surface is not correctly prepared (bottomed out) it may lose its polish.
Granite is not expensive in comparison to other so-called quality materials.
Granite is not difficult to clean, mild soap and water is all that is generally required.

What we have learnt

• Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granites are usually medium to coarsely crystalline, occasionally with some individual crystals larger than the groundmass forming a rock known as porphyry. Granites can be pink to dark gray or even black, depending on their chemistry and mineralogy. Outcrops of granite tend to form tors, and rounded massifs. Granites sometimes occur in circular depressions surrounded by a range of hills, formed by the metamorphic aureole or hornfels.
• Granite is nearly always massive, hard and tough, and it is for this reason it has gained widespread use as a construction stone. The average density of granite is 2.75 g·cm-3 with a range of 1.74 g·cm-3 to 2.80 g·cm-3. The word granite comes from the Latin granum, a grain, in reference to the coarse-grained structure of such a crystalline rock.
• There are, four operations that are involved in the processing of granite. They are: Dressing,Cutting/Sawing,Surface Grinding and Polishing and Edge-Cutting-Trimming. Mining for granite is done manually. For drilling and channeling hand chisels and hammers are used. There are very few quarries that have mining machinery, such as compressors and drilling machines for drilling and blasting, cranes for lifting big blocks, and dampers and trucks for transport.
• Granite has been extensively used as a dimension stone and as flooring tiles in public and commercial buildings and monuments. With increasing amounts of acid rain in parts of the world, granite has begun to supplant marble as a monument material, since it is much more durable. Polished granite is also a popular choice for kitchen countertops due to its high durability and aesthetic qualities. Currently 33% of the kitchen countertops being made are of granite.
• The granite industries involved in cutting, polishing and finishing have some common problems. Most problematic of them are related to stains on the finished products arising out of various factors such as contamination, use of steel pellets, treatments for the machinery, water quality, the quality of granite itself, the environmental factors and many others related to them. The stains on the finished products have a profound effect on production cost and as a whole on the financial side as the stained products cannot be marketed or has to be disposed of at a lower price. Sometimes the pile up of such non-marketable stained products becomes a problem to the company. The company sometimes incur heavy losses due to the same.
• Conventional methods of quarrying granite are becoming increasingly expensive in real and environmental terms. The existing flame torch is, for example, a slow, destructive and noisy method of creating slots. In order to overcome the problems of current equipment, a high pressure water jet slotting device has been developed, field evaluated and is now in commercial production. Water jet cutting has also advantage in secondary preparation of monument stone, where the jets can create straight surfaces and right angled cuts to an adequate level for final surface acceptance.
• Accruent, Inc., the leading provider of contract management solutions, announced today that it closed $12 million in a new round of funding. Accruent has now raised more than $35 million in capital since the company's inception in 1995.
• Finland is one of the major exporters of granite and a world-leader in soapstone production. The annual turnover of the industry is approx. 200 million Euro, divided equally between soapstone and granite products. The value of export is approx. 40% of the turnover. Approx. 200 actively operating companies are found in the line of natural stone business in Finland, employing approx. 2000 persons (with spin-off approx. 3000 persons).
• Granites are now mined in most of the Indian states for use as construction material and road metal but production of dressed granite blocks and slabs from Andhra Pradesh, Karnataka, Rajasthan and Tamil Nadu are highly priced. In India there are 43 granite processing units of which 12 are in Andhra Pradesh, 13 in Karnataka, 3 in Rajasthan, 14 in Tamil Nadu and 1 in Orissa.
• The recovery of marketable grade granite is reported to be 32 to 40 per cent in Karnataka, 25 to 75 per cent in four quarries around Jalore, the main granite mining centre of Rajasthan, and 20 to 40 per cent in Tamil Nadu. Granite exports from India last fiscal were worth Rs 3,018 crore. While Andhra Pradesh accounted for 35 per cent of exports, Tamil Nadu’ share was 33 per cent and Karnataka’s 32 per cent.

Granite

Granite is a common and widely-occurring group of intrusive felsic igneous rocks that forms at great depths and pressures under continents. Granite consists of orthoclase, plagioclase quartz, hornblende, biotite, muscovite and minor accessories such as magnetite, garnet, zircon and apatite minerals. Rarely a pyroxene is present. Ordinary granite always carries a small amount of plagioclase, but when this is absent the rock is referred to as alkali granite. An increasing proportion of plagioclase feldspar causes granite to pass into granodiorite. A rock consisting of equal proportions of orthoclase and plagioclase plus quartz may be considered a quartz monozonite. A granite containing both muscovite and biotite micas is called a binary granite.

The word granite comes from the Latin granum, a grain, in reference to the grained structure of such a crystalline rock.
Granite occurs as stock-like masses and as batholiths often associated with mountain ranges and frequently of great extent. Granite has been intruded into the crust of the Earth during all geologic periods, except perhaps the most recent; much of it is of Precambrian age. Granite is widely distributed throughout the Earth.

Because of its hardness and comparative cheapness in relation to marble, granite is often used to make kitchen countertops. A granite countertop can be cut in any shape, and it is virtually unscratchable. Very hot pots must not be placed onto it though, because the temperature differential could possibly crack the granite.
Average density: 2750 kg/m3 (range 1741 to 2800)

IGNEOUS ROCKS GENERAL
Igneous rocks are crystalline or glassy rocks formed by the cooling and solidification of molten magma. Igneous rocks comprise one of the three principal classes of rocks, the others being metamorphic and sedimentary.
Igneous rocks are formed from the solidification of magma, which is a hot (600 deg.C - 1300 deg.C, or 1100 deg. - 2400 deg. F) molten or partially molten rock material. The Earth is composed predominantly of a large mass of igneous rock with a very thin covering of sedimentary rock. Whereas sedimentary rocks are produced by processes operating mainly at the Earth's surface such as weathering and erosion, igneous--and metamorphic--rocks are formed by internal processes that cannot be directly observed.

Magma is thought to be generated within the asthenosphere (the layer of partially molten rock underlying the Earth's crust) at a depth below about 60-100 kilometers (40-60 miles). Because magma is less dense than the surrounding solid rocks, it rises toward the surface. It may settle within the crust or erupt at the surface from a volcano as a lava flow. Rocks formed from the cooling and solidification of magma deep within the crust are distinct from those erupted at the surface mainly owing to the differences in conditions in the two environments. Within the Earth crust the temperatures and pressures are much higher than at its surface; consequently, the hot magma cools slowly and crystallizes completely. The slow cooling promotes the growth of minerals large enough to be identified visually without the aid of a microscope (called phaneritic, from the Greek phaneros, meaning "visible"). On the other hand, magma erupted at the surface is chilled so quickly that the individual minerals have little or no chance to grow. As a result, the rock is either composed of minerals that can be seen only with the aid of a microscope (called aphanitic, from the Greek aphanes, meaning "invisible") or contains no minerals at all (in the latter case, the rock is composed of glass, which is really a viscous, non-crystalline liquid). This results in two groups of igneous rocks: (1) plutonic or intrusive igneous rocks that solidified deep within the earth and (2) volcanic, or extrusive, igneous rocks formed at the Earth's surface.

The deep-seated plutonic rocks can be exposed at the surface for study only after a long period of weathering or by some tectonic forces that push the crust upward or by a combination of the two. The exposed intrusive rocks are found in a variety of sizes, from small dikes to massive dome-shaped batholiths, which cover hundreds of square miles and make up the cores of many mountain ranges.

Extrusive rocks occur in two forms: (1) as lava flows that flood the land surface much like a river and (2) as fragmented pieces of magma of various sizes (pyroclastic materials), which often are blown through the atmosphere and blanket the Earth's surface upon settling. The coarser pyroclastic materials accumulate around the erupting volcano, but the finest pyroclasts can be found as thin layers located hundreds of miles from the opening. Most lava flows do not travel far from the volcano, but some low-viscosity flows that erupted from long fissures have accumulated in thick sequences. Both intrusive and extrusive magmas have played a vital role in the spreading of the ocean basin, in the formation of the oceanic crust, and in the formation of the continental margins. Igneous processes have been active since the formation of the Earth some 4.6 billion years ago.

IGNEOUS ROCKS MORE DETAILS
Igneous rocks are formed when molten rock (magma derived from the mantle, or, pre-existing rocks molten by extreme temperature) cools and solidifies, with or without crystallization. Over 700 types of igneous rocks have been described, most of them intrusive.
Igneous rock are geologically important because:

• their minerals and global chemistry gives information about the composition of the mantle where they were extracted from, and the temperature and pressure conditions that allowed this extraction, or (below) their minerals and global chemistry gives information about the composition of the country pre-existing rock that melted
• their absolute ages can be obtained from various forms of radiometric dating and thus can be compared to adjacent strata, allowing a time sequence of events
• their features are usually characteristic of a specific tectonic environment, allowing tectonic reconstitutions
• in some special circumstances they host important mineral deposits, of, for example, tungsten, tin or uranium, commonly associated with granites they can be explored as ornamental stone

Igneous rocks are classified according to mode of occurrence, texture, chemical composition, and the geometry of the igneous body.

Modes Of Occurrence
In terms of modes of occurrence, igneous rocks can be either intrusive (plutonic) or extrusive (effusive).

• Intrusive rocks crystallize within the crust interior.
• Extrusive rocks are the result of volcanic eruptions and, therefore, solidify in atmospheric conditions.

Texture
The most important distinction in igneous rocks textures is related to grain size.

• Phaneritic rocks contain minerals with grains (crystals) visible to the unaided eye and are commonly intrusive (as the slower cooling rates allow the formation of large crystals). In the extreme, such rocks may contain extremely large crystals, in which case they are termed pegmatitic.
• In extrusive rocks, where cooling is much more rapid, the individual mineral crystals are usually not visible and these rocks are termed aphanitic.
• Porphyritic textures are an intermediate situation between the previous two: the groundmass of the rock has an aphanitic texture, but crystals (termed in this particular occurrence as phenocrystals) are visible to unaided eye.
• If a molten magma cools at extremely high rates, allowing no crystallization, the result is a vulcanic glass called obsidian.

Crystal Shapes
Crystal shape is also an important factor in the texture of an igneous rock. Crystals may be euedral, subeuedral or anedral:

• Euedral, if the crystallographic shape is preserved
• Subeuedral, if only part is preserved
• Anedral, if the crystal presents no recognizable crystallographic direction

Chemical Composition
Igneous rocks can be subdivided according to two main chemical parameters:
contents of silica:

• acid igneous rocks present a high silica content (ex: granite)
• basic igneous rocks have low silica content (ex: basalt)
• intermediate igneous rocks

contents of quartz, alkali feldspar and feldspatoids: the felsic minerals

• felsic rock, with predominance of felsic minerals; these rocks (ex: granite) are usually light coloured
• mafic rock, with predominance of mafic minerals (all other minerals, excluding the felsic); these rocks (ex: basalt) are usually dark coloured
• ultramaphic rock, with more that 90% of mafic minerals (ex: dunite)

Note that light coloured rocks, such as limestone or sandstone cannot be classified as felsic, because their origin is not igneous, is sedimentary.
The following table is a simple subdivision of igneous rocks according both to their composition and mode of occurrence.

Geometry Of The Igneous Body
Igneous rocks can also classified according to the shape and size of the intrusive body and its relation to the other formations into which it intrudes. Typical intrusive formations are batholiths, laccoliths, sills and dikes. The extrusive types usually are called lavas.

Example Of Classification
Granite is an igneous, intrusive rock (crystallised at depth), with felsic acid composition (rich in silica and with more than 10% of felsic minerals) and phaneritic, subeuedral texture (minerals are visible for the unaided eye and some of them retain original crystallographic shapes).