What is basalt? Geology and Grindstones

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flat black stones paving a road - basalt

A Roman road paved in basalt (This is from Trajan’s Market in Rome)

Basalt is a volcanic stone – it forms from the lava that volcanoes spew out when they erupt. Basalt is a very hard, black stone. It makes a good stone for grinding wheat and barley and millet into flour, and by the Stone Age people who lived in places where there was basalt were already selling basalt grindstones 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.

black shiny stone basalt statue of a naked woman in an Egyptian style

Egyptian basalt statue of Cleopatra (not that Cleopatra, but an earlier one, related to her) from the Hermitage Museum in Russia

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.

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.

a small white blond girl stands next to a hour-glass shaped basalt grinding mill made out of gray stone on a pavement of flat gray stones inside a ruined red brick building

A basalt grain mill from the Roman town of Ostia

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.

More about Roman food

Basalt in Egyptian sculpture

Bibliography and further reading about basalt and volcanoes:

Volcanoes, by Peter Francis and Clive Oppenheimer (second edition 2004).

Why is basalt igneous?
What is Limestone?
What is Tufa?
What is Travertine?
What is Marble?
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By | 2017-05-24T14:33:16+00:00 May 24th, 2017|Architecture, Economy, Geology|0 Comments
Cite this page: Carr, K.E. What is basalt? Geology and Grindstones. Quatr.us Study Guides, May 24, 2017. Web. December 11, 2017.

About the Author:

Karen Carr

Karen Carr is Associate Professor Emerita, Department of History, Portland State University. She holds a doctorate in Classical Art and Archaeology from the University of Michigan. Follow her on Instagram, Pinterest, or Twitter, or buy her book, Vandals to Visigoths.

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