Is basalt smooth or rough?

Basalt: Smooth as Glass or Rough as a Grater? It’s Complicated!

Okay, basalt. We all know it’s that dark, volcanic rock that’s everywhere. But have you ever stopped to really feel it? You might be surprised. Sometimes it feels kinda smooth, almost glassy. Other times? Rough as sandpaper! So, what’s the deal? Is basalt smooth or rough? Well, like most things in geology, the answer is a big, fat “it depends.”

See, basalt is born from lava – that molten rock that erupts from volcanoes. Because it cools relatively quickly at the surface, it usually ends up with a fine-grained texture. Think of it like pouring honey on a cold plate; it sets fast, and the crystals don’t have much time to grow. That’s why fresh basalt can sometimes feel surprisingly smooth to the touch.

But hold on, because that’s not the whole story. Basalt can be a real chameleon when it comes to texture. What makes it rough? A few things:

• Crystal Clumps (Phenocrysts): Imagine throwing a handful of pebbles into that honey before it sets. Those pebbles are like phenocrysts – bigger crystals that were already floating around in the lava. When the basalt hardens, they stick out like, well, like pebbles, making the surface bumpy.
• Bubble Trouble (Vesicles): Lava is full of dissolved gases, like fizz in a soda. As it erupts, those gases try to escape, leaving behind little holes, or vesicles. The more holes, the rougher the rock. Think of scoria – that super-light, hole-y rock you sometimes see in gardens. That’s basalt that’s really bubbly!
• The Weathering Blues: Mother Nature is a master sculptor, and she’s constantly chipping away at rocks. Rain, wind, ice – they all take their toll. Over time, they can dissolve bits of the basalt, creating pits and grooves. I’ve seen basalt columns that started out smooth as glass, but after centuries of weathering, they’re now covered in a maze of tiny cracks and crevices.
• ‘A’ā – Ouch!: Ever been to Hawaii? If you have, you might have encountered ‘A’ā lava. Trust me, you don’t want to walk on it barefoot! This type of basalt lava is thick and pasty, and as it cools, it breaks into jagged, clinker-like blocks. It’s seriously rough stuff!

And it’s not just about the big picture. Even if a piece of basalt looks smooth, put it under a microscope, and you’ll probably see a jumble of tiny mineral grains all tangled together. It’s like looking at a shag carpet – it might feel smooth-ish, but it’s definitely not perfectly flat.

So, why does all this matter? Well, the texture of basalt affects how we use it. Rough basalt is great for things like building sea walls, where you need something that can grip and resist the force of the waves. Smooth basalt might be used for paving stones or even countertops, where you want a more polished look.

The next time you see a piece of basalt, take a moment to really look at it – and feel it! Is it smooth and glassy? Rough and jagged? Chances are, it’s somewhere in between. And that’s what makes this humble volcanic rock so fascinating. It’s a reminder that even the simplest-looking things can have a complex and interesting story to tell.