Igneous rocks are crystalline or glassy rocks formed by the cooling and solidification of molten magma, which is a hot molten material (600-1300 deg C or 1100-2400 deg. F). The earth is composed primarily 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 earths 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 at a depth below 40-60 miles deep, and may settle with the crust or erupting at the surface from either volcano or a lava flow. Rocks formed from the cooling and solidification of magma deep with the crust are very distinct from those erupting at the surface, mainly owing to the difference in conditions in the two environments. Deep below the Earth's surface, liquid magma cooled solidified. Mineral gasses and liquids penetrated into the stone and created beautiful new crystalline formations with a multitude of amazing colors. Primarily composed of quartz (35%), Feldspar (45%) and Potassium, granites usually have darker colors and contain very little calcite.
Igneous rocks are very important geologically because their minerals and global chemical DNA give information about the composition of the mantel where they were actually extracted from. The ages can be obtained from various forms of radiometric dating and can be compared to adjacent strata, allowing a time sequence of events to be calculated. Their diverse features are usually characteristic of a specific tectonic environment. Granites can either be intrusive (plutonic) in nature or extrusive (effusive). Intrusive rocks crystallize within the interior of the earths crust. Extrusive rocks are the result of volcanic eruptions and therefore, solidify in atmospheric conditions.
Sedimentary stones originated from organic elements such as glaciers, rivers, wind, oceans, and plants. Tiny sedimentary pieces broke off from these elements and then accumulated to form large rock beds. They were then bonded through millions of years of intense heat and pressure. Limestone, sandstone, soapstone, fossil stone, shale, chalk and travertine are all sedimentary stones.
ICM sells many European limestones and Travertines. Limestones are in large part composed of calcium carbonate, and are ordinarily light in coloration, but may be colored by impurities, iron oxide making the stone brown, yellow, or red and carbon making it blue, black or gray. The texture in limestones varies from coarse to very fine. Most limestones are formed by the deposition and consolidation of the skeletons of marine invertebrates and many contain lime from sea water. These stones vary in hardness, rarely show much crystalline structure or graining, have an overall smooth granular surface and the more dense types can be polished.
Metamorphic stones originate from the mixture of heat, pressure and minerals which may develop into a crystalline formation, a texture change or a color change. These are the three categories of such stones, marbles, slates and serpentines. Basically marbles are classified into three further categories, dolomite, magnesium or calcite depending on the quantity of magnesium carbonate in the stone. Marble is recrystallized limestone that formed when the limestone softened from heat and pressure and then recrystallized into marble where mineral changes occurred.
The temperatures and pressure necessary to form marble usually destroy all fossils that may have been present in the limestone. The softness of marble and its relative isotropy and marmaros , meaning shining stone. Hundreds of different marbles exit worldwide, including white Alabama marbles, white, pink and gray Georgia marbles, and Green Vermont Marbles. Georgia marbles are used exclusively for veteran tombstones and many important government buildings, due to its extreme hardness factor, perfect for exterior applications due to its non-fading nature.
ICM imports a tremendous amount of slate slabs, which are fine grained metamorphic stones formed from clay, sedimentary rock shale and often quartz. Slate is quarried underground deep within caves primarily from China, India, Brazil, Spain, Portugal, Wales and Italy as well as Vermont, New York, and Pennsylvania. Hundreds of different colored slates now exist, but the premier slate is still considered black slate from Italy, which has been used for thousands of years on rooftops and for billiard tables.
ICM uses only fine Italian slate for our fireplaces, which are all hand cleated with special tools, requiring much skill level to keep the gauging of slate slabs to + or -3.8 to 1/2" thickness. Each slate fireplace imported takes approximately 3 months to import due to the moisture levels within the stone. Brazilian slates are best for outside applications due to their non-fading qualities, but are limited in colors t burgundy, green, rust, grey and black. India is now famous for their amazing vast colors of beautiful slates, but has restricted sizes in such colors of only about 4' lengths of slabs. Longer slab lengths will break when cut. And China, using ancient systems of excavation, often roll their small blocks of slate down a mountain the old fashioned way, without modern technology, making their slates actually very affordable due to the cheap labor costs, yet prone to quality defects if not properly inspected prior to exportation.
Travertines, a form of massive calcium carbonate (CaCO3), are formed through the accumulation of calcite from hot springs or rivers. They contain lots of holes that were formed from water flowing through the stone underground. These holes are usually filled with synthetic resins or cement. They are often beautifully colored and banded (horizontal bands) as a result of the presence of iron compounds or other impurities (i.e. organic). The colors of travertine range from almost pure white (Roman Travertines) to deep mahogany (Iranian Red Travertine). Travertines can be found in numerous finishes from polished to honed and filled, to tumbled, distresses across the vein. This very sturdy stone is an excellent product for any application due to it's elegant look and ease of maintenance.
Creation of Color
Colors of natural stone are affected by their mineral composition. Marble's main consistency is calcium carbonates which is the natural source that bonds the stone. Certain additive minerals blend in to the calcium during formation to customize these brilliant colors. The additive mineral are also interesting color developers present in granite and other natural stones. Stone's brilliant colors and various crystals formations developed when different mineral properties blended together along with the integration of temperature and pressure. The veins and color grains in marble were once liquid minerals that flowed through the stone when the Earth heated up. The intense heat softened the limestone to allow the liquids to flow through it. When the Earth then cooled, the mineral flow stopped and gradually hardened to its current state.
Hardness of stones is another important determination in considering stone's usage for each application. Marble is a relatively soft stone, measuring only 3 out of ten on the Measurement of Hardness Scale (MOHS). Marble is made out of calcium, just like your teeth. If you eat something hard, you all break your tooth. If you eat a lot of sugar, you will get a cavity and stone reacts precisely the same way. If an improper chemical is applied to the surface, corrosion will begin to form cavities in the stone. Listed below is strengths and weaknesses of Hardness (MOH) Scale for stone. This is a guide developed in the 1800s which helps evaluate the strengths and weaknesses of the stone being used. For example, softer stones would require the use of a less active chemical and a more frequent dust mopping program. The delicate colors of natural stones can often be altered by the improper use of cleaning chemicals, mopping with dirty solutions, using chemicals that are not designed for stone care and sunlight which can fade the color easily of natural minerals. Polished stone floors will become dull eventually when heavy foot traffic along with descent and grit erodes the crystals. The pressure from shoes forces the sediment to abrade or fracture the crystals.
Measurement of Hardness Scale
3. Calcite (Most marbles)
6. Feldspar (granites)
7. Quartz (granites)
The objective of the MOH scale is to measure a stones resistance to hardness. When sediment and grit are harder than the surface, they will scratch and harm the stone. For example, a piece of hard plastic is about 2.0. It sill not scratch #3 Calcite or marble. However, a piece of sand that measures a 6, will scratch #3 Calcite but will not scratch #7 Quartz which is granite. The harder the stone, the more resistant to is to abrasion as well as staining. Exterior sediments that are tracked into buildings measures 3.0 to 7.0.
Proper selection of stones for particular applications and then proper stone care is recommended to preserve your stone for years of enjoyment in your home or office. See ICM Stone Care Products to clean up, restore and then properly care for your beautiful stone fireplaces in your home and in commercial spaces. Never use harsh chemicals in cleaning natural stone such ads vinegar and water, use only recommended mild detergents and warm water or ICM approved products to maintain your stone. Stone will survive for several centuries if taken care of properly. Thank you for you interest in the History of Natural Stone and enjoy your ICM products.