Mohs Scale of Hardness Class Activity

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Damian Glenn
6 years ago
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1 Mohs Scale of Hardness Class Activity As we have learned understanding the ground the tunnel will go through is arguably the most important factor in determining your tunnelling method, and to an extent whether a tunnel is a viable and economic option at all. Understanding the ground needs knowledge of both rock and soil but to do this you need an understanding of the minerals that make up the rocks. (The rocks and soils you see around you the mountains, canyons and riverbeds are all made of minerals. A rock is made up of 2 or more minerals.) Believe it or not, in the early 1800s no one had created a system for identifying minerals. That is until a German mineralogist named Mr Friedrich Mohs started to study the different physical properties of minerals as a way to identify them. He noticed that some minerals are very soft, while others are extremely hard. He also observed that harder minerals could scratch softer ones. With this in mind, Friedrich Mohs decided to develop a scratch test where he could determine the hardness of a mineral. To make his scratch test more accurate and helpful, he carefully observed many minerals and created a list of 10 minerals that he arranged from softest to hardest. To this very day we know this list as Mohs Scale of Hardness. The scale is a list of minerals arranged from softest (No. 1) to hardest (No. 10) which is used to determine the hardness of all other minerals and is still commonly used in the field today by engineering geologists when trying to understand the ground conditions a tunnel must pass through and, subsequently, the best design to do so. Points to consider Each mineral can scratch the minerals with lower hardness ratings. Each mineral can scratch itself. Don t press hard, normal scratching should do. Weathered surfaces are softer. Corners or edges of crystals are softer. Small pieces seem softer than large pieces. When you scratch, take a close look at the scratch line which often looks white. Is it really a scratch or is it a powder line made from the tool you used because it was softer than the item you were trying to scratch?

2 TALC MOHS HARDNESS 1 MG3SI4O10(OH)2 USUALLY GREEN, WHITE, GREY, BROWN OR LESS CRUSHED INTO WHITE POWDER KNOWN AS TALCUM POWDER ; PLASTICS; CERAMICS, PAINT

3 GYPSUM MOHS HARDNESS 2 CASO4 2H2O LESS/WHITE/GREY/GREENISH/ YELLOWISH/BROWNISH OR REDDISH PLASTER, AND HOUSEHOLD WALLBOARD, PLASTER OF PARIS

4 CALCITE MOHS HARDNESS 2 CACO3 WHITE/GREY/RED/BROWN/GREEN/BLACK OR LESS OFTEN USED IN SOIL REMEDIATION / STABILISATION AND CONCRETE REPAIR

5 FLUORITE MOHS HARDNESS 4 CAF2 LESS/WHITE/YELLOW/PINK/ RED/BLUE OR BLACK ORNAMENTAL. AS FLUX IN THE MANUFACTURE OF STEEL. IN THE MAKING OF OPALESCENT GLASS. AS ENAMELS FOR COOKING UTENSILS. AS HYDROFLUORIC ACID. AS ELEMENTS IN PLACE OF GLASS IN SOME HIGH PERFORMANCE TELESCOPES AND CAMERA LENS.

6 APATITE MOHS HARDNESS 5 CA5(PO4)3F WHITE/LESS/YELLOW/BLUISH/ REDDISH/BROWN/GREY OR PURPLE THE PRIMARY USE OF APATITE IS IN THE MANUFACTURE OF FERTILIZER IT IS A SOURCE OF PHOSPHORUS. IT IS OCCASIONALLY USED AS A GEMSTONE

7 ORTHOCLASE FELDSPAR MOHS HARDNESS 6 KALSI3O8 WHITE/REDDISH/LESS/YELLOW/ GREY/ORANGE OR GREEN COMMON RAW MATERIAL FOR THE MANUFACTURE OF SOME GLASSES, SOME CERAMICS, SUCH AS PORCELAIN, AND AS A CONSTITUENT OF SCOURING POWDER

8 QUARTZ MOHS HARDNESS 7 SIO2 WHITE/GREY/RED/PURPLE/PINK/ YELLOW/GREEN/BROWN/BLACK OR LESS MOST EARLY STONE TOOLS WERE FASHIONED OF QUARTZ, STAINED GLASS WINDOWS

9 TOPAZ MOHS HARDNESS 8 AL2SIO4(F,OH)2 WHITE/GREY/LESS/YELLOW/BLUISH/ PINK/BROWN OR PURPLE POPULAR GEMSTONE, JEWELLERY

10 CORUNDUM MOHS HARDNESS 9 (AL2O3) BROWN, YELLOW, RED, BLUE OR VIOLET JEWELLERY, SANDPAPER

11 DIAMOND MOHS HARDNESS 10 C LESS/WHITE/GREY/ORANGE/ YELLOW/BROWN/PINK/RED/GREEN OR BLACK USED CHIEFLY AS AN INDUSTRIAL ABRASIVE AND A HIGHLY VALUED SOUGHT AFTER GEM

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