Where does basalt come from?
What is basalt made of?
When the lava cools quickly, it turns into basalt. Usually basalt is black or gray. Basalt is a mixture of feldspar and pyroxene, a rock made mainly of silica and oxygen. Pyroxene is what jade is before metamorphosis.
Is there basalt on other planets?
Why do people want basalt?
Like granite, basalt is a very hard rock. Because it is a common rock and so hard, people used basalt for early choppers and for grinding stones for grinding grains like millet and barley. Basalt makes a good stone for grinding wheat and barley and millet into flour.
Basalt and long-distance trade
Even in the Stone Age, people who lived in places where there was basalt were already selling basalt grindstones (along with igneous obsidian for tools) to their neighbors, and even to people living pretty far away. Basalt is heavy, but people moved it around on boats, so they didn’t have to carry it themselves.
From Sudan north to Egypt
From Sudan, donkey caravans carried basalt grindstones north to ancient Egypt. By the beginning of the Bronze Age, stone carvers in Ancient Egypt also used basalt to make statues. When you polish it, basalt makes very dramatic looking shiny black statues.
Basalt in the Roman Empire
In the Roman Empire, the Romans used basalt for roads, because it was very hard so it would last a long time. They still used basalt for grinding stones, too. Roman traders often shipped basalt (bu-SALT) grinding stones on sailing ships to markets all over the Mediterranean, so people could have good grinding stones even where there weren’t any volcanoes.
New kinds of grindstones
In the Roman Empire, people made more complicated basalt grindstones. This one, shaped like an hourglass set over a cone-shaped piece underneath, is a typical Roman grain mill.
The basalt grain mill is in a bakery, where enslaved people poured wheat or barley in the top of the hourglass (it’s mostly broken off now), and then men or donkeys pushed the top around in circles (see the socket where you can put in a wooden beam to push with?) and the flour came out the bottom, where the little girl’s neck is. This bakery had four or five mills like this one, to make enough flour for all the bread they sold.
How do we use basalt today?
Today, basalt ground up and mixed with oil is a major ingredient in asphalt, and we use it to pave roads.