Rocks, Minerals & Gemstones Quiz — 7 Free Questions

Question 1

What is the name for the breakdown of rock in place at the Earth's surface, by frost prising cracks apart, by heat, by roots, and by rainwater and dissolved gases chemically rotting the minerals, without the debris being carried away?

Question 2

Which fine-grained metamorphic rock, formed by the gentle baking and squeezing of mud rock, splits cleanly into thin, flat, durable sheets along a direction set by the pressure rather than by the original bedding?

Question 3

Which reddish-brown, earthy, lumpy material, not a single mineral but a mixture of aluminium hydroxide minerals, is the world's only commercially important ore of aluminium?

Question 4

Which very common mineral, calcium carbonate, makes up limestone, marble and chalk, fizzes briskly in weak acid, breaks into leaning rhomb-shaped blocks along three cleavage directions, and in its clear form splits an image seen through it into two?

Question 5

Which sedimentary rock consists of rounded pebbles and gravel, at least two millimetres across, set in a finer sandy or muddy matrix and cemented solid, the rounding of the fragments showing they were tumbled along by a river or surf before burial?

Question 6

Which group of silicate minerals splits into extremely thin, flexible, transparent sheets because it has one perfect cleavage direction, and glitters in flakes within granite, schist and many sands, the two common kinds being a pale silvery one and a dark brown-black one?

Question 7

What is the name for the unit of weight used for gemstones, equal to exactly 0.2 of a gram, and divided into 100 'points' so that a quarter-of-a-unit stone is spoken of as 25 points?

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About Rocks, Minerals & Gemstones

Almost everything solid under your feet is a rock, and every rock is a package of minerals. This quiz sorts out the difference and then works through eighty of them, along with the gemstones that are simply minerals rare and beautiful enough to wear. Each question describes something, a rock, a mineral, a gem, a physical property, a shaping process or one of the people who founded the science, and asks you to name it from four choices, then explains what it is, how it forms, how it is identified or used, and the history or misconception attached to it.

The first pack lays the foundations: what makes something a mineral rather than just a solid; what a rock is; the rock cycle that endlessly converts one kind into another; the three great families, born from a melt, built from sediment, or transformed in the solid state; the common members of each, from granite and basalt to sandstone, limestone, marble and slate; the most abundant minerals, quartz, feldspar and mica; and the hardness scale that runs from talc to diamond.

The second pack is the working mineralogy: the tests of cleavage, streak, lustre and specific gravity; the great ore minerals of iron, lead, copper and aluminium; rock-forming and everyday minerals such as calcite, gypsum, halite, graphite, talc, corundum and olivine; the volcanic glass obsidian and the floating rock pumice; the metamorphic trio gneiss, schist and quartzite; geodes, fossils and cave dripstones; the difference between weathering and erosion; and the vocabulary of veins, dikes, foliation and ores.

The third pack is the gem case: diamond and the four Cs; the carat and how it differs from the karat of gold; ruby and sapphire as the two faces of corundum; emerald, aquamarine and the other faces of beryl; amethyst, opal, jade, turquoise, pearl, amber, lapis lazuli, garnet, topaz and peridot; the month birthstones they attach to; the cursed Hope Diamond; the brilliant cut; and the diamond stand-in cubic zirconia. Because a specimen photograph often gives a mineral away to anyone who knows it, pictures are used only where they do not simply hand over the answer, and the most recognisable gems and minerals are left as text. Every figure has been checked, and the wording is kept plain.

Along the way the quiz settles the confusions people carry from school: that a rock and a mineral are not the same thing, one being a mixture and the other a single pure substance; that the 'lead' in a pencil is graphite and contains no lead at all; that fool's gold is pyrite and is lighter, harder and more brittle than the real thing; that weathering breaks rock down where it sits while erosion carries the pieces away; that a stalactite hangs from the ceiling and a stalagmite grows from the floor; that ruby and sapphire are the same mineral in different colours, as are emerald and aquamarine; that the carat which weighs a gem is a different word from the karat which grades gold; and that many historic crown 'rubies' are really spinel. Answers are always a single name chosen from four.