What is Sandstone?
Sandstones consist of arenaceous sedimentary rocks primarily composed of quartz. They contain a common minor component called Feldspar. However, in certain varieties, Feldspar can be a significant component.
What does its color signify?
Sandstone varies in color from grey to red and yellow to white, as sand also comes in different colors. Sandstone cliffs and similar rock formations are easily visible from a distance. Therefore, people strongly identify specific sandstone colors with certain regions. For example, most of West America is famous for its red sandstones.
End-use of Sandstones
It is usually easy to work with sandstones as they are comparatively soft. This unique property makes them a typical building and paving material.
Salient features of Sandstones
Unlike limestone, chalk, or coal which are organic in origin, sandstones are clastic material. Grains like pre-existing rock segments or mineral crystals form the sandstones by cementing themselves together. The types of cement that bind the grains are mostly calcite, clays, and silica. These sand grains come in a size range of 0.1 to 2.0mm. For your information, rocks made of smaller grain sizes include siltstones and shales. People generally call it clay or argillaceous sediments. Similarly, stones made of large grain sizes are breccia and conglomerate rocks, also known as rutaceous sediments.
Sandstone Formation and associated characteristics
Let us now understand the sandstone formation process. The primary mechanism of sandstone formation involves the sedimentation of grains from the water of rivers, lakes, or seas. The deposition environment is an essential element determining the sandstone formation characteristics which include the grain size, composition, and sorting on a micro-level. On a macro level, it refers to the rock geometry of Sandstones.
Broad categories of Sandstones
After you establish the geological characteristics of sandstones, you can then assign them to any of the following three broad categories:
The arkosic category of sandstones has a high feldspar content, which is more than 25%.
Quartzose sandstones, like quartzite, have a high quartz content of more than 90%. Sometimes, geologists also term these sandstones as quartzites, For example, the Tuscarora Quartzite of the Ridge-and-valley Appalachians. However, it is the wrong terminology because quartzite is not a sedimentary rock but a metamorphic rock.
The third category is argillaceous sandstones, such as greywacke. They feature a significant fine-grain element.
What is good about Sandstone?
That was all about the boring scientific stuff about Sandstones. At this point, you might be wondering what is good about Sandstone material. I will possibly answer that with another question: Which Sandstone?
Remember that we cannot classify a sandstone with a one-word label to indicate whether it is suitable for some applications or not. Several sandstones may have drastically different chemical compositions from one another. Even their physical characteristics in the same petrographic group can differ hugely.
Hard Vs. Soft Sandstones
Let us understand these differences with some examples. If you are looking for a heavy-duty application, the stone may have to undergo extensive physical abuse such as hot water, steam, or heavy foot traffic. In this scenario, you can suitably use only quartzose Sandstones, provided that during their formation, they had undergone a substantial amount of heat to make them extremely hard and suitable for above heavy-duty situations. Similarly, some sandstones are more delicate than others. For instance, Arkosic sandstones are much softer than other sandstones, and argillaceous sandstones are the most delicate of all sandstones.
Food for thought
Do you think that your stone dealer will have enough knowledge to help you out with the choice of the application you have in your mind? Probably not. But with knowledge of the above characteristics and salient features of different sandstones, you can make an informed decision.
Bluestone type of Sandstones
Now let us learn about the Bluestone, which is also a part of the sandstone group and one of the most famous rocks intensively mined in the Catskill area of New York State and into Northeastern Pennsylvania. You should not confuse our domestic Bluestone with the Dolerite Bluestone. The famous Stonehenge monument also features these Dolerite Bluestone rocks. You can find them both in Britain (Wales) and Australia (west of Sidney and around Melbourne).