ALL STONE IS NOT CREATED EQUAL – INSIDE STONE
How stone is created is important to understand, because the composition affects its density, absorption rate, hardness and appearance.
Ultimately, these characteristics determine how natural stone should be maintained to keep its beauty for life. Every region of our world is different and therefore contains unique mineral deposits due to the earth’s formation. All stones vary based on where they are quarried or excavated.
The dimensional stones used in commercial applications fall into one of these categories:
SILICAS / SILICEOUS STONE
Silica is the most common mineral on Earth
- Generally hard stone
- Easy to maintain and very durablecarbonates / calcareous Stone
- Next most common rock-forming group
- Generally softer, more porous stone than silica
- Durable, but sensitive to acids (like acid-based cleaners)
Created above and below the Earth’s surface, these stones are commonly believed to have solidified from molten rock (called magma) under pressure. Underground, they are formed when magma becomes trapped in small pockets. As these pockets of magma slowly cool, the magma becomes dense igneous rocks. On the surface, when magma appears above the Earth, it is called lava. As the lava quickly cools above ground, different varieties of igneous rocks form.
A coarse-grained siliceous-based stone of even texture composed chiefly of quartz and feldspar minerals it usually contains small quantities of mica or hornblende. Crystallized at depth, granite masses are exposed at the Earth’s surface by crustal movement or by the erosion of overlying rocks.
- Very hard material
- Easy to maintain
- High density
- Low porosity, but susceptible to staining
OTHER IGNEOUS STONES
Quartz, Obsidian, Pumas
Created from a blend of organic materials; small pieces of our Earth that have been eroded, broken down through the action of glaciers, rivers, wind, oceans and plants. These sedimentary pieces include the skeletal remains of living organisms collected to form rock beds (carbonates). These stones have a variety of combinations.
Wholly or in large part composed of calcium carbonate, it commonly contains minerals and ancient creatures from seawater. Limestone texture varies from coarse to fine and does not show much graining or crystalline structure. It is ordinarily white but may be colored by impurities, iron oxide making it brown, yellow, or red and carbon making it blue, black, or gray. Varies in hardness, Most susceptible to staining.
A variety of limestone and marble that contains holes formed from heat, pressure and water flowing through the stone. These holes are often filled with foreign materials such as cements or resins during the fabrication process to create a flat, polished surface. It is often beautifully colored and banded as a result of the presence of iron compounds or other (e.g., organic) impurities.
OTHER SEDIMENTARY STONES
Sandstone, Gypsum, Conglomerate
The result of the transformation of a pre-existing rock type, in a process called metamorphism, which means “change in form”. The precursor rock is subjected to extreme heat and pressure causing intense physical and/or chemical change. The precursor rock may be sedimentary rock, igneous rock, or another older metamorphic rock.
Metamorphic rocks make up a large part of the Earth’s crust and are classified by texture and by chemical and mineral assembly. They are also formed by the forces of molten rock into solid rock, particularly at the place of contact between the magma and solid rock, where the temperatures are high.
A fine-grained stone formed when sedimentary rocks such as shale are changed by great pressure. Slate splits into wide thin layers. Slate is intermediate in hardness between rocks composed of laminated, often flaky parallel layers of mica and shale.
Marble was once limestone, compacted by heat and pressure that re-crystallized into marble when mineral changes occurred. This produces the colors and veining seen in the stone.
THE DENSITY FACTOR
Hardness is one measure of the strength of stone. The hardness of a stone is relative to the stone’s density. Density can be a factor when considering stone types for a particular project installation.
For example, polished marble can be a beautiful addition to a residential home, but not a shopping mall floor due to the extensive care and maintenance required. The high foot traffic of a mall can eventually dull the surface of polished marble.
MOHS HARDNESS SCALE
Stones hardness can be determined very easily. If a stone can be scratched by a known mineral from the Mohs Hardness Scale list, it is softer than that mineral. If it will scratch another known mineral, then it is harder than that mineral. In this classifi cation, the numbers assigned to objects represent the rank order (1st, 2nd, 3rd etc.) of the entities measured. The variables are called ordinal variables or rank variables. Comparisons of greater and less can be made, in addition to equality and inequality. However, operations such as conventional addition and subtraction are still meaningless.
Extremely dense stones – typically granites – are not as easily scratched, making them suitable for countertop and floor installations. Lower-density stones, such as the calcite-based stones limestone and travertine, are frequently used in lower traffic areas for aesthetics and beauty.There is an easy, practical way to test the hardness of a stone through a scratch test. You may apply this test on the top or back sides of a piece of stone. (Warning: do not conduct this test on the surface of an installed stone – it may ruin the stone.) Using a box knife steel blade, simply score it across the stone’s surface. Do not apply hard pressure. A stone categorized as granite (quartz/feldspar) will not typically scratch. Because granite has a higher tolerance to scratching, it is widely used on countertops. Marble, travertine, limestone or slate will usually scratch fairly easily with a sharp knife.
FABRICATED & APPLIED TEXTURE
Rough stone blocks are extracted from quarries around the world and then shipped to a fabrication plant. The stone blocks are put through a series of processing steps, depending upon the end product desired. These steps include cutting the block into thin slabs, polishing the slabs, and cutting thin slabs into floor tiles or veneer for building exteriors (curtain). Equipment used in fabricating stone includes diamond wire saws, large blade saws with diamond inserts, and saws durable enough to cut thick slabs for monuments. Computer-controlled machines are capable of easily cutting intricate shapes to satisfy the needs of architects and designers.
The fabrication of the stone will affect its porosity and its appearance. There are many types of textures applied or fabricated to dimensional stone surfaces. This list shows some of the more popularly used fabrication methods applied to stone.
A glossy, highly reflective surface
- Surface is very smooth and not very porous
- Polished crystals bring out brilliant colors and grains (400 to 3500 grit to polish stone)
- Shine comes from the natural reflection of the stone’s crystals
- Polish can wear away due to heavy foot traffic and improper maintenance
A slightly rough texture that is achieved by tumbling small pieces of marble, limestone or granite to achieve an old-world/worn appearance
A flat matte to low sheen gloss
- Surface is very smooth, but very porous
- Many more and wider gaps in surface than polished stone
- Medium density
- Commonly used in low traffic areas or for aesthetics
- Colors are not as vibrant as a polished stone
OTHER TEXTURED SURFACES
Pressurized flow of sand and water that results in a matte finish
Rough surface developed through intense heat
Pounding action of hammer develops textured surface. Reduces stone’s color tones
Acid-based cleaners will slowly damage the appearance of calcium-based stone. The acid creates bigger pores for increased staining potential. It also chemically reacts with the stone causing damage and etching. Some household cleaners can be labeled “tile cleaner” or “all-purpose cleaner”, but can still be very acidic and will damage many types of stone and grout.
ACID CAN DAMAGE STONE
Because carbonates (marble, travertine or limestone) react to acid (acidic cleaners) to create carbon dioxide, the effects to the stone are permanent. The destruction of carbonates shows on the surface of stone as etching. Although the particles of stone cannot be recovered, they can be polished or refinished to match the finish of the stone. CaCO3 + acid = CO2 + H2O + Ca2+ Heavy-duty cleaners and strippers containing alkali are ideal for special circumstances requiring deep cleaning – but should only be used on an occasional basis to remove or strip acrylic finishes, waxes, dirt, oil, and penetrating sealers.
REPAIRING ACID & SURFACE DAMAGE
Aqua Mix® have a range of stone restoration products that are designed to repair and restore marble, travertine & limestone surfaces. Aqua Mix® Renue® is a polishing cream that restores the shine of dull, etched or lightly scratched polished natural stone. It is easy to use and no machinery is required. Aqua Mix® Reviver® is a user-friendly, highly-effective, ready-mixed paste for polish restoration and maintenance of worn calcium based polished stone. Ideal for large areas. Aqua Mix® Knockdown® is a non-acidic honing powder that removes light surface scratches, moderate acid etching and wear patterns to produce a flat, even and honed finish. It is excellent for safely honing polished marble, limestone or travertine to a smooth honed surface when a honed, unpolished finish is desired.