Geology of Everyday Stuff and Things: How Tiles are Made

Every morning, you step deep into time, half awake, without thinking much about it.

Steam rises. Water hits stone tiles. Light reflects off the polished surfaces.  You drop the soap...

While the coffee is brewing in the kitchen, really take a look around your shower, or at your bathroom floor.  You might see ancient ocean life, frozen magma, compressed mountain mud, mineral rich hot springs deposits, or engineered earth that's been squeezed and baked.

Let’s follow each type of tile you might find in your shower back to where it began as we learn how tiles are made.

Gray ceramic tiles being installed in a shower

Ceramic & Porcelain Tiles

Long before they were tiles, they were mountains.

Rain fell on granite peaks. Feldspar minerals slowly broke down. Rivers carried the microscopic remains downstream. The sediment settled into quiet basins and floodplains. Over many years, that sediment became clay.

Then humans got involved.

Factories dig up this clay and grind it finer than the natural processes already have. Water is added. The mud is dried into granules. Those granules are pressed under immense mechanical force into tidy tile shapes.

Then comes the kiln.  Inside roaring industrial furnaces, temperatures climb above 1,000°C. Clay mineral structures collapse and reform. Feldspar melts slightly, flowing between particles like lava between stones. Quartz remains rigid, adding strength.

In porcelain, the heat climbs even higher. The tile partially vitrifies, meaning it becomes something close to glass fused with stone.  Porcelain tiles are stronger and denser than regular ceramic tiles, so many people choose porcelain tiles for high traffic areas.  

Pressure and heat cause mineral transformation to happen in a matter of hours.

Your ceramic shower wall might look minimalist and modern, but it’s essentially human-accelerated metamorphism.

Marble & Granite Tiles

Some tiles skip the kiln entirely.  They were already finished by Earth.

Marble: Recycled Sea Life

Picture a warm, shallow ocean long ago. Tiny marine organisms live and die. Their calcium-rich shells accumulate on the seafloor. Layer upon layer piles up and compresses into limestone.

Then continents collide. 

Heat rises. Pressure builds. Minerals recrystallize. Metamorphic processes happen.  The limestone transforms into marble. Veins of iron, graphite, and clay twist through it like frozen lightning.

In places like Carrara, entire mountains are made of this metamorphosed seabed.  There are over 650 marble quarries nearby, and humans have been extracting marble from the area since Roman times.  

When marble becomes shower tiles, humans quarry massive blocks, slice them into slabs, and polish the surfaces.

Sometimes you see the light reflecting off the interlocking calcite crystals, causing the tiles to shimmer!

Granite: Frozen Magma

Now imagine something far more violent.

Molten rock rises beneath Earth’s crust but never erupts. It cools slowly. Crystals grow large. Quartz, feldspar, mica lock together like a mineral mosaic.  This is granite. 

Mountain ranges such as the Sierra Nevada expose vast bodies of this once-hidden magma.

To make granite tile, humans cut blocks from bedrock, slice them into slabs, and polish the surface. 

No kiln required.

Some manufacturers use the term "granite" very um, liberally, and not all granite countertops meet the geological definition of granite.  Planet Geo has a really interesting podcast episode about this that's definitely worth listening to.

Slate Tiles

Slate begins quietly as mud.

Fine sediment settles in calm water. Over time it lithifies and becomes shale. Then tectonic plates collide. Pressure squeezes the rock. Minerals rotate and align.  The rock learns to split apart.  For a cool explanation about the process of slate formation and slate turning into shale using tiles, check out this video.

During the formation of ranges like the Appalachian Mountains, entire layers of shale transformed into slate.  Some good hikes to see shale in its natural environment and other rock outcrops in the Northeastern USA can be found here.

When quarried, slate naturally cleaves into flat sheets along those mineral alignment planes.  No polishing required. The smoothness comes from compression under continental-scale stress.

Slate is not a top choice for shower tiles because it tends to stain easily from shampoo, hair dye, and other products.  Sometimes it also continues flaking apart.  Slate tiles are more commonly used for roofs and floors.  

Travertine Tiles

Now imagine mineral-rich hot water bubbling up through limestone.

As the water reaches the surface, carbon dioxide escapes. Calcium carbonate precipitates out of solution. Layer by layer, mineral deposits build terraces, ledges, and porous stone.  Travertine is stone built by flowing water.

You can see this process today at places like Minerva Terrace at Mammoth Hot Springs in Yellowstone National Park.  Italy and Turkey have major travertine quarries and produce a lot of the travertine used ifor tiles throughout the world today.  

When quarried for tile, blocks are cut from mineral deposits, natural holes are filled, and surfaces are honed smooth. 

The tiny cavities in you see sometimes are fossilized gas bubbles from escaping carbon dioxide.

The Geology Behind Mortar and Grout

It's not just the tiles that have an interesting geological story.  The mortar we use to "glue" them to the wall or floor and the grout we use to fill in the spaces between them are also mostly made from rocks.  

Mortar

Tile mortar (often called thinset) is essentially engineered rock. Its main ingredient is Portland cement, which begins as limestone, a sedimentary rock formed from ancient marine shells. When limestone is heated in a kiln, it transforms into reactive lime, which is then blended with silica and other minerals to create cement.

When you add water, the material doesn’t just “dry.” It undergoes hydration, a chemical reaction where microscopic mineral crystals grow and interlock. This process binds sand grains (usually quartz, one of the most durable minerals on Earth) into a dense, stone-like mass.

Geologically speaking, mortar mimics how sediment turns into rock: loose mineral grains are cemented together into something solid and load-bearing. Its slightly coarser texture and added polymers give it strength and flexibility, making it ideal for bonding tile to a substrate.

Easy to Use Pre-Mixed Delorean Gray Grout with White Subway Tiles

Grout

Grout is closely related to mortar but formulated differently. It uses finer aggregates, or none at all in unsanded versions, allowing it to flow easily into the narrow joints between tiles.

Like mortar, grout hardens through crystal growth during hydration, not simple evaporation. As it cures, it forms a dense, fine-grained cement stone that locks tiles together and protects the edges from moisture and debris.

If mortar is the structural “bedrock” beneath tile, grout is the finishing layer, similar to how mineral-rich fluids fill cracks in rock and solidify over time.

In both cases, tile installation is really a small-scale geological process: heat-altered limestone, water-driven mineral reactions, and quartz grains all coming together to form artificial stone right inside your home.

If you like learning about the geology of everyday stuff and things, check out this article on vintage glassware.

Thanks for reading!  Leave a comment about interesting geology facts you know or questions about rocks in other everyday things.