The famous saying states, to be between a rock and a hard place. But, what about when the rock IS the hard place?
Measuring the hardness of minerals is important in understanding their structural properties and their effectiveness in jewellery applications. The scale we use today is the namesake of German mineralogist, Frederick Mohs, who in the early 1800s, compared the hardness of ten easily accessible minerals. He subsequently charted them, beginning with talc (at the softest rating, 1) and working up to diamond (with a rating of 10, the hardest). The chart is known as the Mohs Scale and remains the standard measure 200 years later. The key to its longevity is in its simplicity. There are no accurate measures of anything simply a ranking scale. The minerals with higher numbers will scratch minerals that rest below them on the scale, however the scale is not weighted. So while diamond (10) is only one grade higher than sapphire (9), it is actually four times as hard.
The table below ranks most of the common gemstones and metals in greater detail:
| Hardness | Type of Mineral |
| 10 | Diamond |
| 9 | Ruby, Sapphire |
| 8 | Emerald, Aquamarine, Topaz |
| 7.5 | Garnet |
| 6.5-7.5 | Steel File |
| 7 | Quartz, Amethyst, Citrine, Agate |
| 6.5 - 7 | Tanzanite, Jadeite, Peridot |
| 6 | Feldspar (Spectrolite) |
| 5.5-6.5 | Most Glass |
| 5 | Apatite |
| 4 - 4.5 | Platinum |
| 4 | Fluorite |
| 3 | Calcite, A Penny |
| 2.5 - 3 | Gold |
| 2.5 | Pearl |
| 2 | Gypsum |
| 1 | Talc |