Marble
Natural Stone History
Where did it come from?
What is it?
Stone is a natural solid formation of one or many minerals. There are thousands of types of stone that have been quarried through the centuries. Quarries are located all around the world. A majority of natural stone comes from Italy, Spain, Turkey, United States, Mexico, China, Taiwan, India, Greece, Canada, France, and Brazil.
The minerals in stone came from the same liquid and gas minerals that formed the earth. The Earth developed as a massive body of gas and liquid minerals that slowly cooled and condensed to a solid core. Through pressure, the Earth's crust began to form and heavy minerals were forced down to the core of the Earth where they were trapped. As the crust got thicker, it squeezed around the inner core, which created intense pressure and heat from within the Earth. Crystals and other solid forms began to grow from the mineral vapors that were being released. As the Earth's crust began to expand and erode, heat and pressure pushed the solid minerals up to the Earth's surface, which formed colossal rock beds. It took up to one hundred million years to from some of these beds. Many of the beds are now used as quarries where the stone is mined.
Most of these minerals can be identified by their color, hardness, and crystal formation. Crystals come in a variety of shapes and sizes. The wide array of these minerals is often difficult to identify. Many stones look very similar to each other; however, they are all very different.
Slate
Slate is a fine-grained rock that can easily be split into thin, durable sheets. It consists mainly of grains of mica and quartz, plus smaller amounts of chlorite, hematite, and other minerals. Most slate is gray to black in color, but the rock may be red or purple depending on its mineral content.
Slate is a metamorphic rock. Most slate is formed below the earth's surface by changes in the makeup and appearance of shale, a sedimentary rock. Shale consists of clay and fine particles of quartz. Heat from deep in the earth changes some of the clay into shale, mica and chlorite. Slate results when pressure created chiefly by mountain-forming movements in the earth's crust, which squeezes the mica and other minerals into parallel layers.
The building industry uses slate for roofing and flagstone because the rock is weatherproof and long lasting. Slate is also used to trim the fronts and lobbies of buildings.
Slate began some four hundred million years ago as sediment at the bottom of ancient seas, and hardened over time forming compressed layers up to seven miles thick. As the continents were squeezed together by ocean rock beneath, these materials were forced upward, creating mountains of slate as it appears today. These natural stones are an incredible building material, known to civilizations throughout the ages for its durability, natural beauty and versatility.
Yes, you should seal your slate. Just as all natural stone applications should be sealed. Though slate varies in porosity, unprotected it can be stained by household products. Choose a high quality sealant that will protect against stains while leaving your slate looking natural. The rule of thumb for re-sealing your surround is that when water no longer beads up, it's time to re-seal. For some folks that's every two years, for some it's four to five years.
Avoid shiny sealant that will show traffic patterns as dull areas. Remember, the low maintenance is one of the attractions of natural slate. In fact, a properly sealed surround only requires periodic sweeping and damp mopping with clean water without soap to protect the sealer.
Slate
Composition: Muscovite Chlorite (wide variation in composition)
Hardness: Soft - easily scratched
Absorption: Low - medium oil, water other liquids
Limitations: Absorbs oils/liquids, cleft planes can spall
Sealer: Sub-surface repellents oil repellent type recommended
Cleaner: Neutral ph detergent or pure soap
Finish: Acrylic OK - wax OK
Notes: Cleft slate is very durable in most situations but quality varies. Slate is typically rustic in appearance but some milled or smooth products are available in some varieties. Wear is typically taken on the peaks or high spots of the textured surface. Acrylics are used when a highly reflective finish is desired. This material is an excellent exterior paving stone. Higher absorbency varieties may not be suitable for exterior areas in freezing climates.
Slate characteristics vary with source. Domestic is typically black, green or mottled (Pennsylvania) and is relatively dense. Many imported slates are available today with wide ranging physical characteristics and overall suitability. Evaluate your stone for density, tensile strength, absorbency, and abrasion resistance. Make sure your slate characteristics are compatible with the intended function.
Surface Textures
Heavy Textures
Natural cleft/ Split face: Rough surface texture, edge rustic
Saw-cut: Rough saw finish, saw marks visible
Flamed: Damp stone spalled by acetylene torch
Sandblasted: Pitted, roughness depends upon grit used
Smooth Textures
Honed: Smooth to the touch but not reflective
Marble
Marble is a rock widely used in buildings, monuments, and sculptures. It consists chiefly of calcite or dolomite, or a combination of these carbonate minerals. Marble is a type of metamorphic rock formed from limestone. Marble is found in many countries, including Belgium, France, Great Britain, Greece, India, Italy, and Spain.
Marble is formed from limestone by heat and pressure in the earth's crust. These forces cause the limestone to change texture and makeup. This process is call recrystallization. Fossilized materials in the limestone, along with its original carbonate minerals, recrystallize and form large, coarse grains of calcite. Impurities present in the limestone during recrystallization affect the mineral composition of the marble that forms. The minerals that result from impurities give marble wide variety of colors. The purest calcite marble is white. Marble containing hematite has a reddish color. Marble that has limonite is yellow, and marble with serpentine is green.
Marble does not split easily into sheets of equal size and must be mined carefully. The rock may shatter if explosives are used. Blocks of marble are mined with channeling machines, which cut grooves and holes in the rock.
Stone Types Marble
Composition: Calcite, Calcium Carbonate
Hardness: Soft
Absorption: Oil, Water
Limitations: Absorbs oil and other liquids, easily scratched, acid sensitive
Sealer: Penetrating type silocane or flouropolymer
Cleaner: Natural Soap or Neutral ph Detergent
Finish: Polished - liquid Paste wax; others: none
Notes: Polished marble is ideal for vertical application but requires a high level of maintenance when used as flooring especially in high traffic situations. Non-reflective finishes perform well as flooring with minimal maintenance once treated with recommended sealers. Kitchen use should be carefully evaluated due to oil absorption.
Granite is a hard, coarse-grained rock that makes up a large part of every continent. Granite contains three main minerals - quartz, alkali feldspar, and plagioclase feldspar. These minerals make granite white, pink, or light gray. Granite also contains small amounts of dark brown, dark-green, or black minerals, such as hornblende and biotite mica. The grains of the minerals in granite are large enough that they can easily be distinguished.
The minerals in granite are interlocked like the pieces of a jigsaw puzzle. Consequently, granite is a strong and durable which makes it useful for construction.
Granite
Composition: Quartz, Feldspar (varies)
Hardness: Hard
Absorption: Varies - Oil, Water
Limitations: Absorbs oils and other liquids, brittle
Sealer: Sub-surface repellents - oil repellent type recommended
Cleaner: Neutral ph detergent or pure soap
Finish: None Normally - Wax OK
Notes: Granite is typical for kitchen counter use. Sealing is recommended for most stones. Granite is the hardest of the polished stones commercially available and is used in high stress situations. Polished granite usually is more absorbent to liquids than many people suppose. Flamed granite surfaces are very absorbent due to the stress fractures in the stone caused by the flaming process and should be sealed if it is desired to maintain the original color and appearance of the stone over time.