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Have you ever walked into a living room, a bath, or a kitchen and wondered where the beautiful stone originated? Or have you ever seen the exterior of a home and wondered how that stone was produced?

Do you love natural stone? Me too. Fans of natural stone countertops, tiles, fireplaces, walls, and building stone are natural allies to geologists. We all share a similar zeal for a glimmer of garnet and the sexy sparkle of marble. The two disciplines have different ways of organizing and thinking about stone, which makes sense because we’re interested in different things.

Natural stones are extracted or quarried from the ground. Granite, marble, limestone, travertine, soapstone, serpentine, onyx, and slate are all-natural stones. The extracting from the earth and the processing of these stones to the final application on a commercial building or a residence is a long procedure. Earth is classified geologically as a stone planet because it is entirely made of stone of various mineral compositions and forms.


There are three classification of stone/rock: Igneous, sedimentary and metamorphic.

Igneous rock

Are formed by the cooling of molten magma on the earth’s surface. The magma, which is brought to the surface through fissures or volcanic eruptions, solidifies at a fast rate. Extrusive igneous rocks (basalt) cool and solidify quicker than intrusiveigneous rocks (granite).

Sedimentary rocks

like limestone and sandstone are formed when sediment is deposited out of air, ice, wind, gravity, or water flows carrying the particles in suspension. Eroded sediments end up in the water and begin to settle (sedimentation). With time, more layers pile up and presses down the lowers layers (compaction). More strata and further compactions forces water out, while salt crystals glue the layers together (cementation).

Metamorphic Rock

Marble, slate & quartzite are formed from any pre-existing rock type like igneous or sedimentary, in the Earth’s crust under variable conditions of high pressures, high temperature, chemistry and time.

After learning how stone/rock is formed, one needs to find the acceptable stone for use in a building material. A sample of the stone is taken by core drilling down at least 10’-20’ for a view of the stone. If the appearance is desirable then the stone should be tested for its strength, absorption, density, and abrasion resistance. These test will help determine the applications of how this material can be physically used. You certainly don’t need to install a highly porous stone in a very wet climate or a soft material in a high traffic area to avoid abrasion of the stone.


There are several types of quarries; open pit, ledge and underground are the most common. In a ledge quarry, the stone is formed in layers where a forklift can remove the sheet of stone or cut small blocks from the hillside or mountain to remove the sheets. In an underground quarry, a tunnel is built underground in order to be able to drive into the tunnel, set up saws and pull the blocks from the wall and remove for processing. The open pit quarry is where saws cut large areas in one direction, maybe a 100’ then turn to crosscut the other direction, maybe 50’.When finished, you will have 150’to pull out of the ground.

Quarry saws are mostly used in open pits for cutting. These saws are like a chain saw with diamond segments. The saws sit on tracks that are level and straight for cutting. Each time the saw finishes a long cut and needs to be moved over or to cut in the opposite direction, the tracks have to moved as well.

The diamonds have to stay cool for the cutting so water has to flow over the segments at all times. If electricity or water is not available, then a generator is used for power and lines have to be laid to the nearest water source and pumped to the saw.

Once a large area is cut, the blocks have to be laid over and split in half. This is done using the old Roman method of feather and wedges. The feathers are placed across the block and wedges are placed in the feathers. They are either drilled with a pneumatic hammer or forced into the feather with a sledgehammer. With the force of the feather and wedges, the block with split in half. This will provide two blocks that are easier to handle. These blocks are ready to be brought above ground for inventory or for immediate processing.


Tech Talk: Anchored Stone

Figure 1. Typically anchored veneer using a split-tail anchor installed in a kerf cut into the bedded surface of the stone. In this case, the backup is a steel stud wall and mechanical anchorage to the backup is accomplished with self-tapping screws.

Anchored stone veneer is an attractive, durable exterior building envelope system and is widely used in commercial and upscale residential buildings. Natural stone units are typical of marble, granite, limestone, or sandstone. Manufactured stone, also known as “cast stone”, often replicates the look of natural stones and can be a cost-effective alternative to natural stone.

Regardless of the unit type, positive anchorage to the backup structure is required for anchored stone veneer. This is typically accomplished with stainless steel anchors that transmit out-of-plane forces such as wind or seismic to the backup. The vertical dead load of the anchored veneer is generally supported by a foundation ledge or shelf angle. Multi-story structures may have a shelf angle or support ledge at each floor line.


The 2015 International Building Code (IBC) identifies two categories of anchored stone veneer – a general class of anchored stone veneer not exceeding 10 inches in thickness and a slab-type veneer not exceeding 2 inches in thickness.

The IBC provides three prescriptive methods for the anchored veneer not exceeding 10 inches in thickness depending on whether the backup is concrete or masonry, wood stud, or steel-stud. All prescriptive methods require a cement grout at least 1 inch thick be placed between the backup and the stone veneer.

For the slab-type anchored veneer, the IBC specifies a minimum of four ties per unit with tie spacing not exceeding 24 inches. The maximum area of a unit is limited to 20 square ft. Veneer ties for slab-type veneer are required to resist, in tension or compression, two times the weight of the anchored veneer.

The IBC also references Building Code Requirements for Masonry Structures, which allows an alternate design method for anchored veneer using general principles of mechanics. This allows more flexibility to adapt the design of the veneer anchors to each unique veneer system. As you can imagine, the IBC’s prescriptive anchorage method for stones up to 10 inches thick is going to be overdesigned for typical veneers that are 2 ¼ to 4 inches in thickness.


The design of stone anchors is straightforward engineering. However, each component, and the connections between them, need to be evaluated for adequate strength and serviceability. For the design of the connection between the anchor and the stone, the engineer may rely on previous experience with a particular stone type or he/she may require that anchor pullout tests be performed on stone samples provided by the supplier.

Anchor tests will provide a range of values for the ultimate pullout force of the particular anchor/stone combination, to which, appropriate factors of safety are then applied. In addition, ASTM C1242, Standard Guide for Selection, Design, and Installation of Dimension Stone Anchoring Systems, provides guidance on design considerations such as stress concentrations, thermal movement, stone durability, and others.

Figure 2. Typical anchor pullout test with a split-tail anchor installed into a semi-circular edge kerf in Lyons Sandstone.


On most anchored stone veneer jobs, multiple anchors are needed to accommodate variable conditions such as outside and inside corners, cavity width variations, soffits, etc. The construction documents should clearly indicate the type of anchor intended for each condition. Minor adjustments can be made in the field to cope with construction tolerances, however, if conditions encountered vary significantly from the design documents, a request for information is definitely needed.


Anchored stone veneer is a common material for exterior building envelopes, however, the anchor system that worked on the last job should not be automatically assumed to work for the next. Each anchored stone veneer system is unique in nature and should be approached as such. Budget for engineering fees to design the anchorages for each job and plan on working closely with your engineer to make sure the constructability aspects are considered as well.

The Art Behind Hardscaping and Paving

Ralph Waldo Emerson

If you were to visit downtown Rock Hill, South Carolina, you might find yourself in the Freedom Walkway, walking on bands of red and cocoa clay pavers from Pine Hall Brick Company, laid into a running bond pattern that stops short to turn into a basket weave pattern at gathering spots.

The design is intended to get visitors to pause for a moment and consider what happened on this spot more than 50 years ago when students from a historically black private junior college took matters in their own hands.

What happened here is best described by what you would see if you looked up. There’s a red brick wall there, emblazoned with the words, “Liberty and Justice For All.”

Standing up for a cause by sitting down

The Freedom Walkway is about the sit-in, an often-used method of civil disobedience in the Civil Rights Movement of the 1960s. Black college students adopted the method of head-on confrontations by going to segregated lunch counters and ordering food. When they were refused, they would stay seated and end up under arrest.

They opted to spend time in jail, rather than pay a fine that would effectively support a system that they saw as unjust. Because the sit-ins were continuing to expand throughout the South, protesters who chose to serve time saved the money that civil rights groups would otherwise have to pay for court fines – and that new strategy again invigorated the movement as it spread across the country.

Art bathroom bluestone carving case study cleaning color commercial cost countertop design education exterior fabrication feel good fireplace floor geology granite healing historical installation interior kitchen landscape limestone marble monument park quarry quartz quartzite remnants residential restoration sandstone selecting slate soapstone sustainability technology trends veneer.

Geologists study rocks to learn more about what happened in Earth’s past. Regular people appreciate rocks because they’re useful, practical, and beautiful. Nonetheless, a bit of geology can shed light on why or where we’d want to use a given stone. Geology also helps us appreciate that every slab of stone offers a little glimpse into deep time and the dramatic forces that shape the planet.


In the world of geology, all stones are related to each other. Over deep spans of time, any rock can turn into a whole new rock if it gets melted, squeezed, uplifted, or eroded. In fact, that’s exactly what’s been happening all through Earth’s history. Understanding the relationships between different stones can make it easier to see why some share similar traits. It also helps you appreciate the events that gave rise to all those beautiful slabs in the showrooms.

Sedimentary rocks turn into metamorphic ones

Limestone forms in shallow, warm oceans and coral-rich beaches. It’s made of shells, shell fragments, and dissolved shells. Limestone can get buried and heated to taffy-like consistency, wherein it turns to marble. Both stones are made of the same mineral – calcite – but in marble’s case the calcite grains have been crystallized together, making the stone less porous. Marble’s distinctive grey streaks are clay layers from the original limestone that got heated and swirled.

The relationship between sandstone and quartzite follows a similar theme. Sand grains gather on beaches, sand dunes, and riverbanks. Layers of sand get buried and pressed together, forming sandstone. If sandstone gets shoved down deep and compressed even further, the sand grains fuse together to become quartzite.

As described in the Deep Dive Into Quartzite article, this process is a gradual one. This means there are many gradations of sandstone and quartzite, ranging from highly porous sandstone to bombproof crystalline quartzite. The more deeply a stone is buried, the more tightly compacted it will get. The porosity of a stone translates into its ability to shrug off stains, and this is something that buyers can evaluate as they shop for different stones.


Bluestone is a variety of sandstone. It formed as rivers flowed off a former mountain range along the eastern seaboard. As 400,000,000-year-old rivers wound their way through the landscape, they left behind pockets of sandstone in Pennsylvania and southern New York. Because the sandy deposits occurred in small, scattered areas, the quarries were small, too, setting the stage for generations of family-run quarrying operations throughout the region.

Dialing up the heat on slate, schist, and gneiss

This trio of rocks shows what happens if you crank up the thermostat on a stone. The predecessor to all of these stones is shale, which is compressed clay and is decidedly un-sexy. But add a little heat and pressure and those unremarkable clay particles start to grow and strengthen and the rock turns into slate. Unlike shale, slate is durable – and is workable into tiles, shingles, and of course, old-school blackboards.

If the stone gets hotter, the clay particles morph into mica and the rock takes on a subtle sheen. This is called phyllite, but in commercial terms phyllite is usually sold as slate. More heat begets even larger mica grains, and the stone becomes schist, which is known for its glittery look. Schists with small mica grains are preferable to stones with large chunks of mica because the latter can be weak and literally flaky.

Adding even more heat and pressure will make the stone separate into bands of light and dark minerals. Striped or banded patterns are the hallmark of gneiss. The patterns can be calm or bold, straight, or swirled. For commercial purposes, gneiss is usually classified as granite, because it’s made of the same minerals, and shares similar properties and colors.

If the stone gets hotter still, it will start to melt. In some slabs of gneiss you can see melted blobs of quartz, showing the stone was right on the edge of becoming liquid again. If the whole thing melts, then you’ll end up with granite, an igneous rock.


Granite means many things. It’s a catch-all category that’s often used to describe any hard, crystalline stone. In geology, granite is one specific thing: an igneous rock that is coarse-grained and overall light-colored. But in the parlance of the natural stone industry, the definition of granite is expanded to include all igneous rocks, as well as many metamorphic rocks like gneiss and schist.

Geologists classify igneous rocks by the size of the crystals and the types of minerals. And while you will definitely sound smart if you casually inquire if your local slab yard has any quartz monzonite or granodiorite, that’s not necessary. Most igneous rocks are quite similar to each other, despite their different colors and patterns. We can just stick to calling them all granite. (Just please don’t tell my geology friends I said this!)

Basalt is one type of igneous rock that is famous for erupting out of volcanoes as the spectacular lava flows from Kilauea we saw last spring and summer. Basalt also makes up the entire ocean crust (which itself is volcanic, betcha didn’t know that!) and forms oceanic islands like Hawaii and Iceland.

Solid rock from liquid water

Onyx and travertine are variations of the same stone. They come about from mineral-laden water as you’d find at the mouth of a hot spring. Both are made of calcite, the same mineral that’s in limestone and marble. Travertine has a lacy pattern from the way the water flows in little rivulets away from the mouth of a hot spring. Onyx can form from either hot or cool water and is less porous than travertine. Onyx is beloved for its smooth layers and gem-like colors that are especially glorious when backlit.

Last but not least: The oddball stone that doesn’t fit into any categories

It’s true with people and it’s true with stones, too. Not everyone fits into a tidy category. Soapstone, for instance, is basically nothing like other rocks. It manages to be soft, yet dense. You can scratch it with your fingernail, but you can’t stain it or burn it, no matter how careless you are. Soapstone is more like a family of stones rather than one specific thing, but it is cool stuff, and I bet it will surprise you

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