Rocks and Minerals
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8correct to beat the crowd
This rocks trivia quiz has 99 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 99 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 when what cools and hardens?
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 03Roughly what share of the Earth's crust, by volume, is igneous rock?
65%
Igneous rock makes up about 65% of the Earth's crust by volume; layered rocks are only about 8 percent by volume despite covering most of the land surface.
Q 04Which rock, formed from compacted mud, makes up about 82 percent of the crust's layered rocks?
Shale
Two other layered rocks account for most of the rest.
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
A fingernail rates about 2.5, so it can scratch talc and gypsum but not calcite.
Q 09Which mineral is number 9 on the Mohs scale, just below diamond?
Corundum
Topaz is 8 and quartz 7; a steel knife blade and window glass both come in around 5.5.
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 bonded in a rigid tetrahedral lattice make diamond; it forms 150 to 250 km down in the mantle and reaches the surface in volcanic rocks called kimberlite.
Q 21The word 'marble' comes from a Greek word meaning what?
Shining stone
Shining stone is the sense of the Greek marmaros, from a verb meaning to sparkle; marble's subsurface scattering of light gives statues their lifelike, waxy glow.
Q 22Which black, polishable form of coal was carved into Victorian mourning jewellery?
Jet
Jet, a dense black fossilised wood related to lignite coal, takes a high polish; Whitby jet became mourning jewellery after Queen Victoria wore it following Prince Albert's death in 1861.
Q 23The 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 14The word 'diamond' comes from the Ancient Greek adamas, meaning what?
Unbreakable
Adamas meant 'Unbreakable' or untameable, a nod to the stone's hardness; diamonds have been known in India for at least 3,000 years.
Q 15How many carats did the Cullinan diamond weigh when dug up in South Africa in 1905?
3,106
The rough Cullinan weighed 3,106 carats and was presented to King Edward VII; its largest cut stone, the 530-carat Great Star of Africa, sits in the Sovereign's Sceptre.
Q 16Which mineral defines hardness 7 on the Mohs scale and keeps time in most modern watches?
Quartz
It is silicon dioxide, the second most common mineral in the crust after feldspar, and the first quartz clock was built in 1927.
Q 17Which mineral group splits into thin, flexible, transparent sheets once used as window panes?
Mica
Mica minerals such as muscovite cleave into thin, flexible, transparent sheets that once served as window panes and as the windows of stoves and lanterns.
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: silica-rich lava that cooled too fast for crystals to grow, and its fractured edges can be many times sharper than a steel scalpel.
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.
Q 24Which geological period takes its name from the Latin word for chalk?
Cretaceous
Cretaceous comes from the Latin creta, chalk, after the thick chalk beds of that age across western Europe; the period ran from about 145 to 66 million years ago.
Q 25Halite, the mineral spread on icy roads, is the natural form of what?
Sodium chloride
Sodium chloride is the chemistry of halite, or rock salt; it forms cubic crystals when seawater evaporates, and the name comes from the Greek hals, salt.
Q 26Coal 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 27Which is the highest-quality rank of coal?
Anthracite
Temperature during formation matters more than pressure or time; in 1700 five-sixths of the world's coal came from Britain.
Q 28A hollow rock lined inside with crystals is called what?
A geode
A geode forms when crystals grow inward from the walls of a cavity; the Pulpí geode in Spain, found in 1999, is about 8 metres long and people can crawl inside it.
Q 29Which 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 30Uluru, 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.