Rocks and Minerals
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8correct to beat the crowd
This rocks trivia quiz has 98 free questions with answers and covers geology from the ground up: the three rock types and the rock cycle, granite and basalt, pumice that floats, obsidian sharp enough for surgery, marble and slate and chalk, the Mohs hardness scale from talc to diamond, why ruby and sapphire are the same mineral, quartz in your watch, halite on the roads, geodes, coal and meteorites. It also takes in the famous rocks of the world, from the Giant's Causeway and Uluru to Devils Tower, the Rosetta Stone and the Cullinan diamond, and the oldest rocks and mineral grains ever found. It is written for school science classes, rockhounds, pub quiz teams and anyone who picked up a shiny pebble on holiday and wanted to know what it was. Easy questions cover the rock types every student learns; the hard ones ask about crustal percentages, kimberlite and the year Friedrich Mohs published his scale. Every answer has been checked against a reliable source and each question shows its citation once you have answered.
30 of 98 questions with answers and explanations. Play the quiz
Q 01Which of these is NOT one of the three main groups of rocks?
Tectonic
Tectonic describes plate movement, not a rock type; the three groups cycle into one another over geological time in the rock cycle.
Q 02Igneous rocks form from which raw material?
Magma or lava
Magma or lava cooling and hardening forms igneous rock; slow cooling deep underground gives coarse-grained granite, while rapid cooling at the surface gives fine-grained rock.
Q 03Which dark volcanic rock makes up most of the ocean floor?
Basalt
Basalt floors nearly all the ocean basins, welling up along the mid-ocean ridges where plates pull apart; it underlies more of Earth's surface than any other rock type.
Q 04Which rock, formed from compacted mud, is the most common of the crust's layered rocks?
Shale
Shale forms when mud is buried and squeezed into thin layers that split apart easily; organic matter trapped in black shale can turn into oil and gas, now tapped by fracking.
Q 05Metamorphic rock forms when existing rock is transformed by heat and pressure without what?
Significant melting
Significant melting would make the result an igneous rock instead; metamorphism alters rock in the solid state at temperatures above roughly 150 to 200 degrees Celsius.
Q 06Silicate minerals make up roughly what proportion of the Earth's crust?
95%
Silicate minerals, built around tetrahedra of one silicon atom bonded to four oxygen atoms, make up about 95% of the Earth's crust.
Q 07The Mohs hardness scale was devised in 1812 by a mineralogist from which country?
Germany
Friedrich Mohs, born in Gernrode in Germany, ranked ten minerals by which could scratch which; the scale is ordinal, so the steps between minerals are far from evenly spaced.
Q 08Which mineral sits at number 1, the softest, on the Mohs scale?
Talc
Talc is so soft that a fingernail scratches it easily; ground to a fine powder, it becomes the talcum powder used in baby powders and cosmetics.
Q 09Which mineral, the stuff of rubies and sapphires, ranks 9 on the Mohs scale, just below diamond?
Corundum
Corundum is plain aluminium oxide: a trace of other metals turns it into ruby or sapphire, while its gritty, impure form is emery, long used as the abrasive on sandpaper and grinding tools.
Q 10Which soft mineral is heated to make plaster of Paris?
Gypsum
Gypsum, a hydrated calcium sulfate, is heated to drive off most of its water and make plaster of Paris; it rates 2 on the Mohs scale, soft enough to scratch with a fingernail.
Q 11Which grey metallic mineral is the principal ore of lead?
Galena
Galena, lead sulfide, is the principal ore of lead; its dense, cubic, metallic-grey crystals also served as the detector in early crystal radio sets.
Q 12Emerald is a green variety of which mineral?
Beryl
Beryl, a beryllium aluminium silicate, becomes emerald when traces of chromium or vanadium colour it green; the same mineral in blue is aquamarine.
Q 13Diamond is a crystalline form of which element?
Carbon
Carbon atoms locked in a rigid lattice make diamond; it forms well over 100 km down in the mantle and is carried to the surface by deep volcanic eruptions, in a rock called kimberlite.
Q 21Which black, polishable form of coal was carved into Victorian mourning jewellery?
Jet
Jet is fossilised wood, a hard variety of lignite coal that takes a glossy polish; carved at Whitby in Yorkshire, it was the fashionable gem for Victorian mourning dress and gave English the phrase 'jet-black'.
Q 22The White Cliffs of Dover are made of chalk, which formed from the remains of what?
Microscopic plankton
Microscopic plankton called coccolithophores shed tiny calcite plates that settled on the sea floor over tens of millions of years, compacting into the chalk of the cliffs.
Q 23Which geological period takes its name from the Latin word for chalk?
Cretaceous
Q 14The word 'diamond' comes from the Ancient Greek adamas, meaning what?
Unbreakable
Unbreakable, or untameable, is how the Greeks understood adamas, their name for the hardest substance imaginable; the same word gives English 'adamant' for someone who will not budge.
Q 15Which diamond, unearthed in South Africa in 1905, is the largest gem-quality rough stone ever found?
The Cullinan
The Cullinan weighed 3,106 carats uncut; it travelled to England by ordinary registered post while detectives guarded a decoy on a steamer, and its largest gem now sits in the Sovereign's Sceptre.
Q 16Which mineral defines hardness 7 on the Mohs scale and keeps time in most modern watches?
Quartz
Quartz hums at a steady rate when electricity passes through it, so a sliver cut to vibrate 32,768 times a second lets a watch chip count off each second.
Q 17Which mineral group splits into thin, flexible, transparent sheets once used as window panes?
Mica
Mica peels into sheets because its atoms bond tightly within each layer but only weakly between layers; heatproof and non-conducting, it glazed stove windows and still insulates electrical parts.
Q 18Which volcanic rock has so many gas bubbles that it floats on water?
Pumice
Pumice is frothy volcanic rock whose trapped gas bubbles make it less dense than water; pumice stones are also used to stone-wash jeans and to scrub skin.
Q 19Obsidian is a natural volcanic what?
Glass
Glass is what obsidian is: it cooled too fast for crystals to grow, and its fractured edges are thinner and sharper than surgical steel, so obsidian blades are still fitted to some scalpels.
Q 20Marble is the metamorphosed form of which rock?
Limestone
Limestone recrystallises under heat and pressure into marble; Michelangelo carved Carrara marble from Tuscany, and the Parthenon was built of Pentelic marble from near Athens.
Cretaceous comes from creta, Latin for chalk: Belgian geologist d'Omalius d'Halloy coined it in 1822 for the thick chalk beds of the Paris Basin, and the period ended with the extinction of the dinosaurs.
Q 24Halite, the mineral spread on icy roads, is the natural form of which compound?
Sodium chloride
Sodium chloride is the chemistry of halite, or rock salt; it crystallises in cubes where seawater or salt lakes evaporate, leaving thick beds that are mined for road and table salt.
Q 25Coal is classed as what kind of rock?
Sedimentary
Sedimentary rock is coal's class: it forms from layers of plant matter buried and compressed in ancient swamps over millions of years, which is why seams often hold fossil leaves.
Q 26Which is the highest-quality rank of coal?
Anthracite
Anthracite tops the coal ranks because the most heat and pressure acted on it, driving off most of its moisture and gases, so it generally gives the most heat per tonne of any coal.
Q 27A hollow rock lined inside with crystals is called what?
A geode
A geode begins as a cavity, often a gas bubble in volcanic rock; mineral-rich water seeps in and crystals grow inward from the walls, so a dull, lumpy outside can hide a glittering lining.
Q 28Which ore rock is the world's main source of aluminium?
Bauxite
Bauxite, named after Les Baux in southern France where it was first described in 1821, is refined into alumina and then smelted into aluminium metal.
Q 29Uluru, the giant monolith in central Australia, is made of what kind of rock?
Sandstone
Sandstone of a coarse, iron-stained kind called arkose makes up Uluru, which rises 348 metres above the plain and glows red at dawn and dusk; climbing was banned in 2019.
Q 30Which rock formation became the first US National Monument in 1906?
Devils Tower
Devils Tower in Wyoming was proclaimed by Theodore Roosevelt; Kiowa and Lakota stories hold that the deep grooves running down its sides are the marks of bear claws.