40 Fun Facts About Pumice

Which volcano's 1883 explosion left pumice rafts adrift, tree trunks and all, for up to 20 years?

Krakatoa threw out so much pumice that in places the floating raft stood 1.5 metres above the waves. Ships reported huge fields of it for months afterwards.

Which Roman landmark did engineers lighten by adding more pumice to the concrete as they built higher?

The Pantheon's dome is still the world's largest unreinforced concrete dome, almost 2,000 years on. Light pumice and tufa at the very top keep its weight down.

Which clothing gets its faded, worn-in look from being tumbled with pumice stones in a rotating drum?

Denim jeans are stone-washed with pumice, which also softens the stiff cloth. The catch is that each pair wears out sooner.

Which soft-furred pet rodent keeps clean by rolling in a bath of fine pumice dust a few times a week?

A chinchilla should not bathe in water, because its fur can mat and grow mould. The animals take to their pumice dust baths by instinct.

Pumice was once called spuma maris in Latin because people believed it was hardened what?

Sea foam seemed a fair guess for a pale stone found bobbing on the waves. Around 80 BC the Romans also knew it as lapis spongiae, for its sponge-like holes.

In ancient Rome, powdered pumice was a gritty ingredient in which everyday hygiene product?

Toothpaste with finely ground pumice has been sold in modern times too, because the grit strips plaque easily. It is too abrasive to use every day, though.

Which heavy-duty hand soap bar, first made in St. Louis in 1893, contains ground pumice?

Lava takes its name from the ground volcanic pumice in every bar. The WD-40 Company, better known for its spray lubricant, bought the brand in 1999.

Astrobiologists have proposed drifting pumice rafts as an ideal setting for which event on early Earth?

The origin of life needs a busy surface, and pumice rafts have the highest surface-area-to-volume ratio of any rock type. They also drift for years, soaking up useful chemicals.

Which Roman city did pumice from Vesuvius rain on in 79 AD, collapsing roofs before the deadly surges?

Pompeii lay downwind, so the pumice fell there while upwind Herculaneum was spared at first. The stones piled up until roofs gave way.

A pumice raft mistaken for land may explain which phantom isle near New Caledonia, mapped from 1876?

Sandy Island stayed on charts, Google Maps included, until an Australian research ship sailed through the spot in 2012. The whaler Velocity may have logged a pumice raft as dry land.

Lipari holds pale pumice and which dark, glassy rock that Stone Age toolmakers traded as far as Croatia?

Obsidian from Lipari was worked into fine bladelets by the late Neolithic and traded to Sicily and the Po valley. The island is covered in both rocks.

Which darker, denser volcanic rock, also known as cinder, usually sinks in water where pumice floats?

Scoria has bigger bubbles with thicker walls than pumice, which makes it heavier. It builds the steep little cinder cones found on many volcanic fields.

A pumice raft covering 26,000 square kilometres was spotted in 2012 by which Pacific country's navy?

New Zealand's navy met the raft near Raoul Island, with pumice blocks poking 60 centimetres above the surface. Its possible source, the Havre Seamount, had erupted unseen on the seabed weeks earlier.

Pumice rafts from undersea eruptions near Tonga in 1979, 1984 and 2006 all drifted west to which nation?

Fiji lies about 350 kilometres west of the Tongan volcano behind the 2006 raft. Some of the earlier rafts were reportedly 30 kilometres wide.

Corals have crossed the Pacific from Tonga on drifting pumice rafts to reach which World Heritage site?

The Great Barrier Reef is a long ride away: pumice tracked after one Tongan eruption drifted more than 3,000 kilometres west. Biologists think plants and animals hop between islands the same way.

What sudden change makes gas fizz out of rising magma to form pumice, as when a soda bottle is opened?

A drop in pressure frees the dissolved gas, and rapid cooling then freezes the bubbles in place before they can escape. Both have to happen at once.

Which Philippine volcano's 1991 eruption, the 20th century's second-largest, rained white pumice?

Mount Pinatubo emptied so much magma that its summit collapsed into a hollow. The haze it threw into the sky cooled the whole planet by about half a degree Celsius.

Which Cascade Range volcano sent out flows of glowing pumice bombs in a 1980 eruption that killed 57?

St. Helens produced two kinds of pumice in 1980: a white type that is about 86 percent bubbles and a denser grey type. It remains the costliest eruption in US history.

What are towering, pumice-rich eruptions like Vesuvius in 79 AD called, in honour of a Roman eyewitness?

Plinian eruptions are named for Pliny the Younger, who described Vesuvius in a letter after the eruption killed his uncle. They punch columns of debris into the stratosphere.

On which Greek island are houses extended with rooms dug sideways into pumice, cool all summer?

Santorini closed its pumice quarries in 1986 to protect its caldera. The air-filled rock insulates so well that the dug-out rooms stay warm in winter too.

Scribes rubbed pumice powder into which writing surface while it was wet and stretched on its frame?

Parchment took ink more deeply once pumice powder had smoothed its flesh side. Early bookmakers also used the stone to finish leather bindings.

Ancient Egyptians used pumice stones, razors and creams to remove what, partly to control lice?

Body hair was removed all over in ancient Egypt, as a form of ritual purification as well as pest control.

During a salon pedicure, a pumice stone rubs dead skin and which hardened patches off the feet?

Calluses were being smoothed with pumice in ancient China, where the stones also kept fingernails groomed.

Ancient Chinese medicine added ground pumice, mica and fossil bones to which drink to calm the spirit?

Tea laced with ground pumice was prescribed for dizziness, nausea, insomnia and anxiety. Healers believed that swallowing powdered rock could soften lumps inside the patient.

Around 1680, an English naturalist noted that pumice powder was used to bring on which reflex?

Sneezing was one of many odd jobs given to pumice by early doctors. In the 18th century, pumice ground as fine as sugar went into remedies for ulcers of the skin and eye.

A pumice stone on a handle is a household tool for scrubbing limescale rings off fixtures made of what?

Porcelain bathroom fixtures can be scrubbed with a pumice stone, which also shifts rust and hard water rings.

Gardeners mix pumice into potting soil to suit cacti and which other drought-hardy plants?

Succulents thrive because pumice lets water and gases pass through its pores while storing nutrients in the tiny holes. It does not rot, and it does not attract fungi or insects.

Pumice is the gritty abrasive mixed into the rubber of which everyday desk item, often coloured pink?

Erasers owe an older debt to pumice too: before rubber, writers scraped ink mistakes away with bits of the rough stone. The first widely sold rubber ones appeared in 1770.

Pozzolana, the volcanic ash and pumice Romans mixed with lime, takes its name from a town near which city?

Naples lies close to Pozzuoli, whose volcanic sand Vitruvius recommended for mortar around 25 BC. He gave a separate recipe for work under water.

Pumice-rich flows from the 1912 Novarupta eruption filled which US state's Valley of Ten Thousand Smokes?

Alaska's Novarupta eruption was the largest of the 20th century. Explorer Robert Griggs named the valley in 1916 for the thousands of steam vents rising from the fresh deposits.

Which country's Puyehue-Cordón Caulle volcano dumped ash and pumice on Argentine towns in 2011?

Chile's eruption threw out an estimated hundred million tons of ash, sand and pumice. The cloud circled the Southern Hemisphere and grounded flights as far away as Australia.

Tube pumice, with bubbles stretched into long parallel pipes, closely resembles which natural material?

Wood is such a close match that geologists also call the rock woody pumice, as well as fibrous or pipe pumice. The stretching happens as the bubbly magma is drawn up the volcano's conduit.

What do geologists call the gas-bubble cavities that riddle pumice and make up most of its volume?

Vesicles fill 64 to 85 percent of a typical pumice, which is why it weighs so little. Their walls are thin, translucent films of natural glass.

Which ancient people farmed moisture-holding patches of pumice in the Jemez Mountains of New Mexico?

Ancestral Puebloans chose ground covered by the El Cajete Pumice, which likely held more water than the soil around it and suited their crops.

Most pumice shares its silica-rich makeup with which pale rock, the erupted equivalent of granite?

Rhyolite is the most silica-rich of volcanic rocks, which makes its magma extremely stiff. Gas cannot slip out of such sticky melt, so the bubbles stay trapped as it hardens.

Lipari, whose pale pumice is shipped worldwide, is the largest of which archipelago north of Sicily?

The Aeolian Islands are said to be named after Aeolus, the mythical ruler of the winds. The 1984 film Kaos ends with children sliding down Lipari's white pumice slopes into the water.

Pumice from Japan's 2021 Fukutoku-Okanoba eruption drifted over 1,000 km to clog ports in which prefecture?

Okinawa had 11 ports damaged by the drifting pebbles, which also hurt fishing and tourism. The eruption had happened two months earlier, near South Iwo Jima.

A pumice-rich deposit called the Diliman Tuff lies beneath which Southeast Asian capital city?

Manila's pumice bed is a puzzle, because the volcano that produced it has not been identified. Its chemistry rules out the nearby Taal and Laguna calderas.

Because pumice lies loose at the surface, miners can skip which noisy step that hard-rock quarries rely on?

Blasting is unnecessary because the rock sits in loose heaps, so bulldozers and power shovels can simply scoop it up. That makes pumice one of the gentler things to mine.

Pumice lumps count as which catch-all term for every fragment a volcano throws out, whatever its size?

Tephra covers everything from fine ash to blocks, and its buried layers work as time markers. Geologists and archaeologists date sites by matching a layer to one known eruption.