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Natural Granite

Where Does Granite Come From

What is Granite

The definition of granite from a geological standpoint is "any plutonic rock in which the mineral quartz is 10 to 50 % of the felsic components, and the ratio of alkali to total feldspar, is between 65 and 95 %." Commercially, any holocrystalline quartz-bearing plutonic rock is generally included in the granite rock grouping.

Why Granite

Granite is considered to be one of the most versatile types of natural stone available. Tiles slabs and countertops are available in a wide range of granite colors. Natural stone fabricators or granite fabricators, can custom-tailor the stone to the aesthetic or performance requirements requested.

Granite Scratch Resistance

Granite rocks are one of the hardest stones on earth and offers outstanding durability. Its resistance to scratching, are largely dependent upon the hardness of the minerals that make up the stone. In most granite rocks, the primary minerals are quartz and feldspars, accounting for approximately 90% of the rock. The hardness of a product or mineral can be defined by use of Moh's Scale. This scale lists 10 substances or minerals in ascending order of scratch resistance:


1. Talc
2. Gypsum
3. Calcite
4. Fluorite
5. Apatite
6. Titanium
7. Quartz
8. Topaz
9. Corundum
10. Aggregated Diamond Nanorods


This scale can be expanded by adding other minerals or common materials with scratch resistance that is similar to those minerals originally cited.

1. Sulpher, Talc
2. Amber, Gypsum
2½ Fingernail
3. Calcite, Pearl (3-4), Coral (3-4)
3½ Copper penny
4. Fluorspar, Rhodochrosite, Fluorsprite
5. Apatite, Turquoise (5-6)
5½ Opal, Steel knife blade
6. Feldspar
6½ Hardened steel file, Common window glass
7. Quartz, Garnet, Beryl
8. Topaz
9. Corundum
10. Diamond

Granite Hardness

It should be noted that the above scales are of "relative" hardness, and not linear. For example, there is significantly less difference between 7 and 8 on the list, than there is between 9 and 10. The scale tells us that a mineral that can be scratched with a fingernail has a hardness of less than 2½. Minerals that can be scratched with a pocketknife, but not with a penny, offer a hardness of between 3½ and 5½. Quartz and Feldspar, with hardness of 6 & 7 respectively, are the minerals that give granite its exceptional abrasion resistance.

Granite Stability

Granite offers excellent dimensional stability. In fact, it is so good, that granite is the material of choice for many precision applications such as machine mounts, surface plates and press rolls, where tolerances can be measured in micro-inches (millionths of an inch). Granite, just like any solid, will expand and contract with changes in temperature. This change is relatively small. The coefficient of linear thermal expansion of granite is typically in the neighborhood of 4.4 x 10-6 inches per inch per degree Fahrenheit. In the perspective of common stone panels, this means that a 5' 0" panel would change dimension by approximately 0.026" in a 100°F temperature change. Granite will typically return to its original dimension when the original temperature is reestablished. Permanent strain, or failure to return to its original dimension will not normally occur unless the material has been heated to excessive temperatures (above 480°F ).

Granite Acid Resistance

Industrial processing vats containing sulfuric acid, hydrochloric acid, nitric acid, and bromine are commonly lined with granite panels, taking advantage of the material's natural resistance to these caustic chemicals. This level of chemical resistance contributes to the ability of granite to resist attack from airborne pollutants associated with acid rain and/or snow-melting chemicals. Certainly there are chemicals that will attack granite, but exposure to them in a typical building environment would be extremely rare.

Granite Flexural Strength

Flexural strength, or the ability to resist bending force, is a factor that determines the allowable span of a dimension stone panel in a given thickness subjected to given loads. Flexural strength varies amongst different types of granite, and typically is between 1,000 and 2,000 lbs/in². This allows the use of "thin" (30 mm) panels for many applications, minimizing both curtain wall cost and dead load for the building frame. Thicker granite panels (15/8" [40 mm], 2" [50 mm] or greater) are available where spans or loads necessitate their use.

Granite Water Absorption

For applications that are below grade or in contact with soil, water absorption is an important property. Absorption rates of granites range from 0.10% and 0.40% by weight. Furthermore, most granite materials will effectively allow water to evacuate during freezing cycles to prevent surface damage from the freezing water. Repetitive freeze/thaw cycles, particularly saturated cycles, will result in a reduction of strength in the granite panel. This loss can be significant, perhaps 20%. Laboratory experiments have shown that the strength loss occurs most aggressively in the first 100 cycles, after which the strength loss is much slower paced.

 

Table of Dimensional Stone Test Values per ASTM Standard Specifications

 

 

Absorption
(max)
per ASTM C 97

Density
(min)
per ASTM C 97

Modulus of
Rupture (min)
ASTM C 99(9)(10)

Compressive
Strength (min)
ASTM C 170

Abrasion
Resistance (min)
ASTM C 241

Flexural
Strength (min)
ASTM C 880

Stone Type

ASTM Standard

%

lbs/ft3

kg/m3

lbs/in2

Mpa

lbs/in2

Mpa

Ha

lbs/in2

Mpa

Granite

ASTM C 615

0.40%

160

2,560

1,500

10.34

19,000

131

25

1,200

8.27

Marble

ASTM C 503

0.20%

162

2,590

1,000

6.89

7,500

52

10

1,000

6.89

Limestone(1)

ASTM C 568

12.00%

110

1,760

400

2.76

1,800

12

10

n/a

n/a

Limestone(2)

ASTM C 568

7.50%

135

2,160

500

3.45

4,000

28

10

n/a

n/a

Limestone(3)

ASTM C 568

3.00%

160

2,560

1,000

6.89

8,000

55

10

n/a

n/a

Quartz-Based(4)

ASTM C 616

8.00%

125

2,000

350

2.41

4,000

28

2

n/a

n/a

Quartz-Based(5)

ASTM C 616

3.00%

150

2,400

1,000

6.89

10,000

69

8

n/a

n/a

Quartz-Based(6)

ASTM C 616

1.00%

160

2,560

2,000

13.79

20,000

138

8

n/a

n/a

Slate(7)

ASTM C 629

0.25%

n/a

n/a

9,000

62.05

n/a

n/a

8

n/a

n/a

Slate(8)

ASTM C 629

0.45%

n/a

n/a

7,200

49.64

n/a

n/a

8

n/a

n/a

 

Frequently Asked Questions About Granite
 
Supreme Surface will service marble and granite countertops and other quality surfaces to all of Indiana including the following cities.