Tag Archives: travertine

Unusual Fossil Occurrence in Travertine

A number of years ago, when I was an undergraduate student, I had the privilege of going with my adviser on many trips in the field. I learned more on those trips than I think I did in the classroom. On one trip he took me to several hot springs in the Black Rock desert of central Utah, and I got to observe the deposition of travertine first-hand.

Black Rock travertine

Black Rock travertine

Travertine is a carbonate deposit most often associated with hot springs. As the water travels through the Earth and is heated by some deep, magma source, and then circulates back to the surface, it dissolves a host of minerals. On the surface, through either evaporation or the action of microbes the minerals precipitate out of the water, slowly building up layer upon layer of stone. The vesicles and contaminates of the travertine give is unique and interesting texture, and thus make it a popular decorative stone for tiles.
Several years prior to my visit with my professor, he was there with another student and they studied the travertine and hot springs of the region, and they found the remains of a fossil bird, an American Avocet, preserved in the stone. It seems that the bird had died in one of the hot springs, and the travertine formed around the bird’s skeleton, preserving impressions of feathers as well as the bones of the body.

American Avocet skeleton preserved in travertine

American Avocet skeleton preserved in travertine

In addition to the bird, remains of insects in the travertine were common. These fossils give new meaning to the term set in stone.

For other stories on travertine, see:
An introduction to travertine tiles
Advice on installing travertine tiles

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What’s the difference between igneous, metamorphic, and sedimentary rocks?

There is something basic in our desire to classify things. Early humans no doubt looked around them at the natural world and instinctively began to group, and subgroup, things. Maybe they grouped things that flew, things that swam, things with leaves, or whatever. And, we have been doing it ever since, trying to create a taxonomy of the natural world that helps us to make sense of it.

Trouble is, our taxonomies are always a best guess, or an approximation, of nature, and this is very evident in the three major groups of rocks. Introductory geology students are usually taught about igneous, metamorphic, and sedimentary rocks, but this really is an oversimplification of nature.

Igneous rocks are those that form from a full melt, where the mineral material is completely turned to a liquid state. From a hot, liquid state, the mix is cooled at various rates and under various conditions to create a variety of igneous rocks. If the mixture cools underground, we call the liquid rock magma, and the rock that forms from it is called an intrusive igneous rock. If the liquid comes to the surface and cools faster, we call it lava, and the rock is an extrusive igneous rock.

Sedimentary rocks generally start with any of the already-formed rock types, and through weathering, transport, and re-deposition, lay down new rock combinations. For example, weathering of a rock may form sand-sized grains that get transported to a beach where it is later solidified into a rock called sandstone. There are other common sedimentary rocks like shale, siltstone, and limestone.

Metamorphic rocks are the hardest to understand in concept, I think. This process is similar to igneous in that it involves heat to cook the rock, but for metamorphic rocks the process does not progress to a full melt of liquid rock. Instead, the heat, and often high pressures of geologic processes, transforms the mineral and rock structure. This is common in mountain-building processes, where the intense pressure of tectonic plates colliding squeezes the rock with immense pressures.

Geologists name the layers of rock that we map to help unravel geologic history. There is a whole code for the naming of rock formations.

But this neat taxonomy of igneous, metamorphic, and sedimentary is not always clear-cut. Many rock types are really a combination of processes; we should not expect that nature falls into our simple categories. Take ash fall deposits for example. Ash is spewed from volcanoes during an eruption (an igneous process) and then blown across the landscape, often forming very thick deposits (a sedimentary process). There are several examples of ash like this across the Central Plains, far from where the ash originated. One prime example is at Ash Fall State Park in central Nebraska where a herd of rhinos was buried by a thick ash deposit.

Travertine is another rock that has a mixed origin. Water is heated at depth by proximity to magma (igneous) and picks up minerals. The water can then travel to the surface where it cools and deposits the minerals layer upon layer (sedimentary), building up travertine. This rock often has interesting texture and colors due to mineral impurities, making it a nice decorative stone used for tiles.

So, we start with basic guidelines as way to understand geologic processes. I have described this as “lying” to intro students, not maliciously, but by giving them principles that are true enough, but oversimplified. If you go on in geology you spend the rest of your education learning the exceptions to the rules.

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Advice on Installing Travertine Tiles

Tiles come in a wide variety of materials. No matter what material is chosen, installation has these basic steps. One of the first requirements is a solid and firm base. A mastic or mud bed is spread on the firm base to hold the tile in place. The tiles are then laid on the mud to form the desired pattern. The mud is allowed to dry before a grout is spread to fill the spaces between the tiles. A sealer is applied to the entire area to prevent discoloration of the grout and the tile.
The above statements apply to all forms of tiles. Installing travertine follows the regular rules plus a few that are specific to a natural stone and a veined material.

One of the considerations when working with travertine tile is the veining of the stone. A commonly used method of shaping man-made tiles is by using a “score and snap device”. This method does not work with travertine. The natural travertine is porous, and may have those pores filled with a special mixture of cement and epoxy. The combination of the stone and filler gives the tile an irregular density that requires a power tool to cut the tile. The veins that run through the travertine add another complication for the installer. The veins are a natural “weakness” lines in the stone. Cuts can be made across the veins, but experience working with travertine will help guide a installer to prevent unwanted breaks both at the time of setting and later.

Black Rock travertine

Black Rock travertine

The tiles are cut from natural stone. The stone will vary from quarry to quarry and cutting results in some irregularities in the thickness and shape of the tiles. Most of the irregularities can be adjusted by the way the tile is laid. Again, an experienced tile setter will adjust the mud bed to compensate for variation in thickness, and can position the tiles to conceal the size differences.

Because the stone is a natural product and no two tiles will be the same, the coloration in the stone will vary a great deal. Some of the tiles will have many veins and others little or none. It is highly recommended that you open and inspect all the boxes of tiles to allow the installer and the homeowner to view the stone and lay out a pattern that is most pleasing. This will also allow the installer to select the best tiles to cut before the job is started. This could save time and money because fewer tiles are ruined. In many cases laying out the whole area will be well worth the time.

Most installers feel that sealing the tile is a must. Sealing the stone is a simple way to assure the tile will remain beautiful. Re-sealing the tile every few years is also recommended. The routine care and maintenance is best done with clear water.

Mild soaps can be used but harsh cleaners and acids should never be used. The calcium carbonate of the travertine will react with even weak acids and dissolve. This will cause the stone to etch and could cause significant and irreversible damage. If you are uncertain you can test any cleaner on a sample tile reserved for that purpose before you use anything on the installed tiles.

Related posts:
Introduction to Travertine Tiles
Unusual Occurrence of a Fossil in Travertine

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