Kafka Architectural Aggregates Color Chart

How Does Natural Stone Get Its Color?

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No two pieces of natural stone look alike—even if you’re comparing two pieces of granite extracted from the same quarry. This variation of color, pattern, and texture is part of what makes natural stone so unique and so highly prized as a building and landscaping material. If you’re on the lookout, you’ll notice it in a variety of projects, from chimney facades to public pathways. Currently, thin stone veneer is a particularly popular natural stone product for both commercial and residential projects.

But how, exactly, does natural stone get those striking colors, and why can’t you find the color you’re looking for in your area? Geology holds the answer to these and further questions.

What Causes Color Variations in Natural Stone?

When it comes to color variations in natural stone, it’s all about minerals. Take Wisconsin, for example. Kafka Granite’s home state has glacially deposited minerals to thank for the wide range of colors we see in our local stone quarries.

Minerals and other organic components that were present when rocks were being formed resulted in the rainbow of different colors that we see today. The exact arrangement and abundance of said components are what create the beautiful graining, textures, and varied hues that natural stone is so well known for.

Those various minerals and organic compounds all have different properties and chemical makeups, meaning that they all affect natural stone in different ways. Iron oxide, for example, creates a vivid red color, while serpentine can create a green coloration in stones like marble. The abundance of the mineral deposit will also determine how varied the colors are in a particular stone. You might be able to clearly see a mineral deposit in stone extracted from a certain part of a quarry, while other areas contain lesser amounts of the mineral and therefore fewer bursts of color.

Here’s a look at how minerals affect the hues of several common types of natural stone.

Granite

Granite, primarily composed of minerals and rocks like quartz and mica, is found in a wide range of colors across the country. An abundance of potassium feldspar will give a deposit of granite a warm, pink hue, while the presence of quartz will create that classic, milky-white tone. Thanks to its glistening tones, granite is an excellent option for interior and exterior thin stone veneer projects.

Marble

With zero impurities present, marble is largely white and uniform—but you’d be hard pressed to find any significant amount of naturally occurring marble that doesn’t contain color variations. The striking veined patterns that make marble such a popular natural stone are caused by deposits like feldspar and iron oxide.

Quartz

Quartz is a naturally clear stone, so the presence of any impurities will change its appearance. You’ll find this stone in just about every color you can imagine, although some are more common than others. Purple, yellow, and gray are just some of the hues you’ll come across when purchasing quartz stone products. 

Why Can’t I Find a Specific Color of Stone in My Area?

If you’re looking for a specific color of natural stone for your project, the good news is that there’s an immense variety of colors out there. The bad news is that you might find your own options somewhat limited, depending on the area from which you’re trying to source materials. 

Wisconsin’s unique geology makes it rich in naturally occurring decomposed granite, along with quartz and feldspar. But other areas of the country may lack some types of natural stone entirely, or they may have an overabundance of one color. The solution, then, is to locate a supplier of high-quality natural stone products, one who can source the color that matches your design.

Kafka Granite’s Natural Stone Products

Kafka Granite is proud to offer natural stone products in dozens of dazzling colors. We have so many hues on hand because our immediate area is rich in the mineral deposits that create them. As we mentioned, our state of Wisconsin is known for its naturally occurring decomposed granite in fiery reds and golds—but that’s not all we have to offer. We’ve spent over 40 years scouring the country for different colors of natural stone. 

Today, we source our natural stone products from quarries across North America. This allows us to offer a color and product selection that you simply won’t find anywhere else. So if you’re wondering why you can’t find pink granite or anything other than gray limestone when sourcing materials for your next project, now you know: your area likely doesn’t have any deposits of the type or color of natural stone you’re on the hunt for. But if you have your heart set on a specific color for your installation, we’d be happy to help. 

Looking for the Perfect Color of Natural Stone for Your Next Project?

If you’re having a hard time finding the right natural stone for your project, don’t settle. Instead, contact Kafka Granite today. Architects, designers, stonemasons, and more come to us for our extensive selection of specialty aggregates, thin stone veneer, and other natural stone products. If you’re not quite sure what you’re looking for, our knowledgeable sales team is here to help. We look forward to helping you incorporate the beauty of natural stone into your next project.

Quality Control 101: What Is Specific Gravity?

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So far, in our quality control series, we’ve discussed Mohs hardness and absorption—but there are still many other factors that play a role in creating specialty aggregates, natural thin stone veneer, and other products that will last. Today, we’re diving into the importance of specific gravity and bulk specific gravity in stone. Let’s take a look at what this physical property can tell us, why it’s so important, and how it’s measured.

What Is Specific Gravity?

Specific gravity is a ratio of the mass of a substance to the mass of the same volume of liquid (typically distilled water). This physical property plays an important role across a wide range of processes, from biological processes like kidney function to product performance. 

You may have also heard this property referred to as “relative density.” The word “relative” should hint at the fact that specific gravity is a unitless measurement. To make sense of this property, measurements must be compared against a standard. For solids and liquids, that standard is water at its most dense (about 39 degrees Fahrenheit), while gases are measured against room temperature air.

As water is the typical standard, it is understood to have a specific gravity of 1. A specific gravity below 1 indicates that a substance is less dense than water and will therefore float in the liquid, while a specific gravity greater than 1 means that the substance is more dense and will sink. Specific gravity in natural stone ranges from 2 to 3, meaning that stone is two to three times denser than water.  

Water Absorption and Bulk Specific Gravity in Stone

Specific gravity doesn’t exist in a vacuum, however; when it comes to the performance of natural stone products, other physical properties must be accounted for. Water absorption and specific gravity are two properties that go hand in hand.

All types of natural stone are porous to some degree, meaning that they will absorb a certain amount of water. Absorption allows us to assess that porosity, which in turn allows us to evaluate how well a stone will withstand weathering and structural stress. In general, denser stone is less porous. Because water absorption is measured as a percent by weight, however, a low-density and high-density stone can have the same absorption capacity—but the higher-density stone will actually absorb more water by volume. 

To allow for this caveat, we measure bulk specific gravity. This property takes into account a stone’s absorption capacity, giving us a better understanding of how strong the resulting product will be, how it might be affected by the freeze-thaw cycle and other natural forces, and what it can realistically be used for.

Specific Gravity and Quality Control

So, how does specific gravity in stone relate back to quality control? When it comes to natural stone products, consistency is key. Specialty aggregates used in architectural precast, decorative precast, and other manufactured products need to meet specifications for a particular application or installation. At Kafka Granite, we make key measurements like Mohs hardness, specific gravity, and absorption available directly to our customers, so that they can make the most informed decisions when sourcing materials for their projects.

Even non-load bearing products like natural thin stone veneer have to hold up to the installation process, the elements (if exterior), and forces like heat and changes in humidity. This means that every masonry unit needs to fit into an acceptable range of physical properties, from Mohs hardness to bulk specific gravity. 

How Is Specific Gravity in Stone Tested?

It’s not enough to simply be aware of standards—those standards need to be met every time. Kafka Granite adheres to ASTM material specifications for our stone products. Samples of our dimension stone are sent out for a number of tests, including ASTM C97: Standard Test Methods for Absorption and Bulk Specific Gravity of Dimension Stone. This particular assessment is used to measure both absorption capacity and bulk specific gravity for all types of dimension stone except slate. 

Absorption is up first. At least five test specimens are dried for 48 hours in an oven to ensure they’re completely free of moisture. Their dry weight is recorded, and they are then submerged in water for another 48 hours to make sure they’ve naturally reached their absorption capacity. When fully saturated, the samples are weighed again. The percentage difference between these two values is the absorption capacity.

To determine bulk specific gravity, the saturated specimen is suspended by a wire in air and weighed. The process is repeated with the stone suspended in water. The difference between these two values is the bulk specific gravity, which can then be used to determine density.

The testing process is similar for our specialty aggregates, but it’s important to note that, unlike dimension stone, aggregate or crushed stone isn’t required to conform to any one standard. However, this data determines whether crushed stone is appropriate for a specific application—so it still needs to be collected. Samples of our specialty aggregates are subjected to a similar process of drying, soaking, and weighing to determine both their absorption and specific gravity.

Kafka Granite’s Commitment to Excellence in Stone Products

Our decades of experience in the industry have made it clear to us that architects, designers, stonemasons, and others need high-quality specialty aggregates and masonry units that will hold up under stress and against natural forces. At Kafka Granite, we’re committed to providing consistent, useful products that fit perfectly into a project. If you’re searching for thin stone veneer or other natural stone products, reach out today. We’re always happy to answer any questions you may have.

Quality Control 101: What Is Absorption?

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Here at Kafka Granite, we’re dedicated to providing high-quality stone products—but that’s not the only thing that makes us an industry leader. Our dedicated team is constantly seeking out colorful new deposits and developing innovative uses for natural stone and products to meet the ongoing needs of our customers. We’re also happy to share our technical knowledge. To that end, we’re diving into the next topic in our quality control series: absorption. 

In previous installments, we’ve talked about the overall importance of quality control, dug a little deeper into Mohs hardness, and specific gravity. Now, we’ll be looking at what absorption is, how it’s measured, and why it matters to the end-user.

Why Does Absorption Matter?

Absorption is the percent by weight increase in the mass of a material when water is absorbed into its pores. (This does not include any water adhering to the surface of the material.) This acts as a measure of a stone’s porosity, which can tell us quite a lot about how durable that stone will be for a particular installation.

If you’re wondering exactly why water absorption matters in natural stone products, know that it all comes back to quality control. Different absorption levels determine how well a specific type of stone will withstand weathering and structural stress, and, by extension, how a product can be used. It’s essential that the qualities of a stone match the needs of the application; otherwise, your project simply won’t last.

Absorption capacity is particularly important in natural stone products that will be exposed to the elements and undergo the freeze-thaw cycle. If you’re creating a building facade from natural stone, for example, you’ll need to select an appropriate type of stone—one that is durable and not overly porous. If your material absorbs too much water, you’ll find it much more vulnerable to freezing weather. 

As another example, if you’re sourcing decorative aggregates for the face mix of your pavers, you should opt for an aggregate mix with a lower absorption. Continued freeze-thaw cycles and other forces will make aggregates with higher absorption levels more likely to break down over time, eventually compromising the integrity of the paver itself.

Finally, absorption can also tell us about a stone’s stain resistance. To protect the integrity of your installation and reduce the risk of your material becoming stained over time, it’s essential to choose a stone with a low water absorption.

How Do You Test for Water Absorption of Stone?

Water Absorption of Dimension Stone

Dimensional stone sold for commercial use must meet certain criteria across a number of categories, including absorption, specific gravity, and compressive strength.

ASTM International is a non-profit organization that develops both material standards and testing methods for products and materials throughout numerous industries. ASTM C97: Standard Test Methods for Absorption and Bulk Specific Gravity of Dimension Stone is used to test absorption capacity for a variety of types of dimension stone, such as marble and granite. 

Here’s a brief look at how the test progresses:

  • Five or more test specimens are prepared.
  • The samples are dried in an oven for 48 hours to ensure they are completely free of excess moisture. 
  • When totally dry, the specimens are weighed.
  • Next, the samples are submerged in water for another 48 hours to make sure they’ve naturally reached their absorption capacity.
  • When completely saturated, the samples are weighed again.

The absorption capacity of each sample is determined by calculating the difference between the fully dry and fully saturated weights. The resulting value, expressed as a percentage, gives us one piece of the puzzle for determining whether a type of stone is appropriate for a specific application.

Along with testing methods, there are ASTM specifications to which natural stone products must adhere. The standard requirement for water absorption in granite, for example, is .4 percent, while marble is .2 percent. 

It’s important to note that the absorption capacity of each type of dimension stone is actually a range, rather than one number. Absorption capacity in granite typically ranges from .8 to .01 percent, while marble goes from .8 to .04 percent. This means that a portion of natural stone sold on the market will fall outside of ASTM specifications. 

This brings us back to the essential nature of quality control. Remember that the most affordable option may not be the best option for your project—in fact, specifying low-quality natural stone products may actually end up costing you more in repairs and replacements in the long run. If you ever find yourself in doubt, be sure to ask your supplier for proof of ASTM testing.

Water Absorption of Crushed Stone

Our crushed stone is also regularly tested for absorption, Mohs Hardness, and specific gravity. But unlike dimension stone, there is no universal standard for water absorption of aggregate or crushed stone. Instead, organizations or businesses typically have specifications for materials they use in different projects. The Wisconsin Department of Transportation, for example, has a set standard for epoxy overlay aggregates. It’s essential that materials used in projects like high-friction surfacing installation meet these specifications. Otherwise, the aggregate will break down—reducing traction and failing to perform. 

To ensure that an aggregate meets the requirements for a particular application, samples are tested according to ASTM standards, such as ASTM C127: Standard Test Method for Relative Density (Specific Gravity) and Absorption of Coarse Aggregate. 

The method for testing water absorption in aggregate or crushed stone is similar to that of dimension stone:

  • Aggregate samples are first dried to remove any excess moisture.
  • Once dry, the oven-dry density of the aggregate is measured.
  • Next, the samples are soaked in water for a prescribed period to ensure that they reach maximum absorption capacity.
  • Finally, the soaked samples are used to determine the saturated-surface-dry density and absorption.

High-Quality Stone Products From Kafka Granite

When you purchase specialty aggregates or other natural stone products from Kafka Granite, you can rest easy knowing the materials you receive will be of the highest quality. To further demonstrate our commitment to transparency and quality, all test data is available to our customers upon request.

We pride ourselves on our attention to detail and continuous pursuit of excellence—and we’re always happy to discuss your newest project. If you have any questions about our range of products or specifications, feel free to contact us today.