Hardness of Rocks and Minerals Quiz

The Mohs scale, named for its creator, German geologist Friedrich Mohs, compares the hardness of minerals based on the ability of one mineral to make visible scratches on another.

As the softest of all the minerals, the best that talc (hydrated magnesium silicate) can do is leave a white streak when scraped over a plate (which almost every silicate mineral can do). Talc has a variety of uses, including being ground to make talcum powder and baby powder; as a food additive and in the manufacture of paper, amongst other things.

Sitting at the second spot on the Mohs scale is gypsum (calcium sulfate dihydrate). The many uses of this relatively soft mineral include as a component of fertilizers, various plasters and drywall applications and even blackboard chalk. It is mined in many countries worldwide, with China in the forefront in 2015, though other countries have greater reserves.

Copper and silver also fall into the same range as gold on the Mohs scale, that is between 2.5 and 3. Pearls and amber are also in this group, making it seem the home of many precious metals and desirable items. Gold rushes in various parts of the world have provided colourful historic incidents, as well as wealth for the lucky prospectors.

Fluorite, or fluorspar, is the reference mineral for number four on the Mohs scale. One of its uses is as a flux, or flowing agent, in iron smelting. Other minerals with a hardness of four include iron, nickel and the magnificently named heazlewoodite, a rare nickel sulfide.

Turquoise sits between 5.5 and six on the Mohs scale, along with opal and other less familiar minerals. The colour turquoise gets its name from the bluish-green variety of the mineral, but the latter can occur in a range of hues including powder blue and sky blue. One of the earliest gems to be mined, old world sources include Iran, while the southwest United States is an important new world source.

Sitting at 6.5 on the Mohs scale, the element silicon is described as hard, brittle and crystalline with a blue-grey sheen. Historically used in the manufacture of industrial compounds like cement, concrete and various forms of glass, silicon's more modern usefulness has been in the field of computers and smartphones.

Occupying a position between seven and seven and a half on the Mohs scale, garnet is a gemstone with a name derived from a Middle English word meaning "dark red". Although red garnets are what most think of first, other colours of the stone do exist. Garnet dust is also useful in industry as an abrasive for use in sandblasting or in finishing wooden furniture (in sandpaper form).

Beryl, and its varieties aquamarine and emerald, are classified between 7.5 and eight on the Mohs scale. It is quite a common mineral found in various parts of the world, and comes in a range of colours, with red being the most rare. In 13th century Italy, beryl was used to make the very first lenses for eyeglasses.

The reference mineral for nine on the Mohs scale is corundum, which is aluminium oxide in crystalline form. Pure corundum has no colour, but its varieties may. The gem variety ruby is red, due to the presence of chromium, and sapphires come in a number of colours (though NOT red).

At last we come to the hardest of the hard, the diamond, the item on the scale that defines the number ten. Diamonds are a crystal form of carbon, and are highly prized as gem stones, though they have industrial uses as well. The hardness of diamonds makes them ideal for use as drill bits, for example.