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History of Stone:
Granite stone is hewn from the earth and is extremely
dense yet also porous. Once it is cut and polished it must be sealed to prevent
stains. Its very permanence makes it difficult to work and shape, but
technological advances have made it possible to cut and polish stone near
quarries around the world, a money-saving development that enables unusable
pieces to be discovered before they are shipped abroad.
Granite is cut with diamond saws, then polished like glass and shipped around
the world where it becomes the most cosmopolitan of counters. It exists
everywhere in the world, yet nowhere is it the same. Even from the same quarry,
no two pieces are identical.
Granite, the most popular stone for counters, is an extremely hard rock formed
by volcanic activity. Its shimmering beauty lies in the crystals of quartz,
mica, and feldspar trapped within. So-called consistent granite has the same
pattern throughout. Variegated granite has veins that vary from piece to piece,
which add character but also it difficult to match sections.
Soapstone and slate are much softer than granite but also less porous. Slate was
formed from clay on ancient sea beds and generally has a solid gray, black, or
green hue. Soapstone, which is composed primarily of the mineral talc, has a
similar color but often contains light striations of quartz. Both stones scratch
and chip easily, especially on the edges; the marks can be sanded out or left to
add character. Combined with a sink of the same material, slate or soapstone
counters can create a classic farmhouse look or a sleek, refined look. It's not
generally necessary to seal these stones, but a periodic application of mineral
oil will make them glow.
Marble and limestone are warm and soft but less practical for kitchens because
food acids stain them readily. Still, many homeowners don't mind stains that add
a patina of age. And marble is a classic surface for rolling out pastry; serious
bakers often include a section of marble countertop in their kitchens for this
purpose. Marble is generally polished like granite; limestone is often honed to
a matte finish.
What Is Granite:
Granite - Earth’s Oldest Building Material
Granite is—quite literally—as old as the earth. It is formed from liquid magma,
the molten rock still found at the core of the planet, cooled slowly to form a
substance approaching the hardness and durability of diamond. Granite is an
igneous rock, the name reflecting its fiery beginnings. The chemical composition
of granite is similar to that of lava. However, granite owes its hardness and
density to the fact that it has been solidified deep within the earth, under
extreme pressure. Over the eons, seismic activity has changed the crust of the
planet, forcing veins of granite to the surface. Glaciers scraped off layers of
dirt, sand and rock to expose granite formations. Typically revealed by
outcrops, the deposits have been discovered on all the continents.
Composition
It is accurate to speak of "granites," because many varieties of the stone
exist. While they differ in color, texture and crystalline structure, the
granites have three essential minerals in common: Feldspar, Quartz, and Mica.
These minerals occur in different proportions, giving each granite slab its own
color, texture and structural characteristics. In addition, hornblende,
magnetite, hematite, pyrite, zircon, garnet, corundum and other minerals may be
present in smaller amounts, adding to the unique coloration and texture of each
granite deposit. In supplying granite for a large building or complex of
buildings, it is essential that the stone be consistent in color and texture. To
assure this, each granite color must be quarried from the same deposit. With
natural material like granite, a certain amount of "movement" or grain in the
stone must be expected. Many people find this flow and blending of colors to be
the most compelling reason for using granite.
Physical Properties of Building Stone:
Expansion – Weathering - Permeability
All stones are natural materials subject to variation in properties according to
specific mineral composition, size and thickness of the tested piece.
Coefficient of Expansion
Stone expands and contracts minimally with temperature change. Normally the
amount of change is too insignificant to cause a problem. However, some of the
purest marbles retain a small incremental change after each heating cycle. This
is called hysteresis. In thin veneers, it can put strain on the backing material
and cause bowing and even rupture. This also increases the porosity of the
stone, making it more susceptible to attack from atmospheric acids and cyclic
freezing. In granite and limestone, the amount of change is in millionths of an
inch—usually not enough to cause problems. In some marbles and sandstones, the
coefficient is in hundred-thousandths of an inch, which could cause problems. In
most construction systems, the normal fasteners and joint materials accommodate
minor expansion and contraction of the stone.
Weathering
Stone generally weathers better than other building materials; however, not all
stone endures equally well. Some are subject to greater damage from freezing and
thawing and attack from sulfurous and sulfuric acid, carbonic acid and ammonium
salts. Granite is nearly impervious to weathering from temperature changes and
from airborne chemicals. In fact, granite is so resistant to chemical erosion
that granite tanks are often used to store highly caustic materials.
Freeze/thaw weathering rarely occurs in polished granite surfaces. Weather
damage to granite with any finish is extremely uncommon because of its
inherently low absorption rate.
Permeability
Granite is significantly less porous than other building stones, yet it is
capable of absorbing moisture. Fabrication is a "wet" process: the cutting of
granite is accomplished with a slurry of water and abrasive material. Sometimes
granite is shipped before it is completely dried, and the moisture absorbed
during fabrication gives the granite a different color than in its dry state.
Such stones will dry in relatively short order and return to their true color.
Once dry, the atmospheric moisture precipitation and humidity will not normally
penetrate the stone.
Variegation
Granite is very consistent in color and texture when compared to marble;
however, granite also exhibits movement and color variation.
Comparing Granite To Other Building Materials:
All Stone Is Not The Same...
There are several different types of building stone on the current market. At
The Granite Gallery, they include common stone such as granite, marble,
limestone, travertine, as well as the man-made CaesarStone™. Each stone has
unique physical characteristics, which affect its applicability to various
building designs. This section describes the characteristics and physical
properties of the major building stones.
Granite
Granite is an igneous rock created deep within the earth from magma, cooled
slowly under great pressure. It is the hardest building stone with very dense
grain, making it virtually impervious to stain. It takes a highly polished
finish, which will endure even in inclement environments. It also can be
finished in a variety of other ways. There is a broad spectrum of granite colors
ranging from nearly pure white to nearly pure black. During its formation,
granite may also have been infused with other minerals providing patterned
"movement" as well as color.
Most common uses: Interior and exterior wall cladding, interior and exterior
paving, residential & commercial counter tops, monuments, curbing, statuary,
balance tables, novelty items, etc.
Marble
Marble is a metamorphic rock, composed of metamorphosized limestone. In its
purest form, marble is crystalline white calcite. Most marbles, however, are
infused with impurities such as dolomite, silica or clay, providing variations
in color and significant movement. The base colors of marble range from white to
black with a broad range of hues. Marble is significantly softer than granite
and therefore subject to greater wear and weathering.
Most common uses: Interior and exterior wall cladding, Interior and exterior
paving, Fireplace facing and hearth, Lavatory tops, Residential & Commercial
counter tops, Table Tops, Statuary, Novelty items, Many non architectural uses,
such as tooth paste, paint whiting, agricultural lime, etc.
Limestone
Limestone is a sedimentary rock composed of calcites and dolomites. Organic
limestones were formed from the deposits of marine shellfish and fossils.
Limestone is non-crystalline and possesses very uniform composition, texture and
structure. It is soft and therefore easy to quarry and shape. Limestone ranges
in color from white to gray and does not take a polish.
Most common uses: Interior and exterior wall cladding, interior and exterior
paving, limited counter top use.
Engineered Stone
Most engineered stone is a quartz aggregate bound with a polyester resin. It is
very hard but there are question in the industry about the absorption of liquids
over time.
Most common uses: Kitchen countertops & backsplash, bath vanity tops, tabletops,
fireplace surround.
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