Limestone vs Onyx

Two very distinct natural stone materials with interesting traits. Both limestone and onyx are interesting and have a lot to offer in the way of design and practical use. The characteristics of each though, may be of a surprise to you. In this article, we will take a look at these materials and compare their qualities. As we do, we will also mention some practical uses in which each of them are beneficial. Let's get into our match up of limestone vs. onyx.

Comparing Composition

The minerals of which natural stone are made impact the uses, appearance, and even durability of it. In the case of the two materials we are considering in this article, both are made up largely of calcium carbonate. In other words, both limestone and onyx (banded calcite, geologically speaking) are what is known as calcareous stone. But let's take a look at these to see how the two stones differ.

Limestone is Sedimentary

Natural limestone is a sedimentary rock that forms in aquatic environments such as oceans. It forms when minerals precipitate out of water containing dissolved calcium. It is a natural stone that is relatively easy to cut due to its hardness and is very practical for certain uses which we will talk about momentarily.

Onyx is Metamorphic

The term "onyx" is used in different ways, so let's clarify what we mean here. We are using the term in the commercial sense. Commercial stone industry terms differ from geologic nomenclature. Onyx, to a geologist is not the same thing as banded calcite. Banded calcite is what we are calling "onyx".

Onyx (or banded calcite) is a metamorphic rock. Like limestone, onyx precipitates in an aquatic environment. However, instead of forming underwater, it forms on the surface of the earth. When the minerals precipitate out, a crust of calcite crystals form. The end result of this repeated process is a stone with bands of color and calcite. The color is caused impurities and the the purest calcite is white or clear in appearance.

How Limestone & Onyx Are Used

Even though these materials are made up of the same main mineral, how they form results in differing appearances. Because of the difference in their appearance and traits, they work well for different applications. Let's consider some use for each of these materials.

Uses for Limestone

Because of its composition, limestone is a effective covering for surfaces. It does well in a number of environments. Although it is used for countertops and vanities, it is a very effective material when used as a surface cover in the form of wall tiles, floor tiles, and even pool decking. Wait, pool decking?

Because limestone is porous it readily absorbs water and other liquids. When you think about the environment around a swimming pool, there is a lot of water that gets on the surface. If the decking around the pool is non-absorbent, the water stays on the surface and creates a slip hazard. But limestone "drinks" up the water. And if the tiles are left unpolished, the surface is not slippery. Yes, limestone is a very practical natural stone. What about onyx though?

How Onyx Is Used

Natural stone is a beautiful material. And onyx is no exception when it comes to beauty. The colored bands in a slab of onyx can be a variety of color, but they are most frequently a golden or brownish color. These intriguing bands of color in an otherwise white or clear stone add visual interest to its appearance.

Another spectacular trait commonly found in onyx is translucency. This property allows light to pass through the stone in some areas. The result? A magnificent display of color when it is backlit. Because of this trait, onyx slabs are used for bars and other surfaces through which backlighting is shone. Backlit onyx is an astounding method for creating focal points.

Working and Caring for Calcareous Stone

As we stated above, both limestone and onyx are calcareous natural stone materials. This means that these rocks are relatively soft and they react with acid. That means 1) you want to use blade for cutting marble when you work with them and 2) they will etch if used in an environment where there is acid-based liquid. So, having an effective etch remover on hand is a good idea so you can correct blemishes that result.

As we have seen in this article pitting limestone vs onyx, these materials offer much in the way of beauty and practicality. Depending on your project, you may find that one or the other is a good fit for the job. As we have seen though, they have a number of similarities and yet they can be used for very different purposes.