The Geological Society of Hong Kong 香港地質學會


Bits and Pieces

Hardness Box DIY


Mohs’ Hardness Scale is a useful mean for the identification of mineral in the field.  Although it cannot determine the absolute value of hardness of individual minerals, the principle of comparing soft and hard materials helps to eliminate many possibilities of like minerals.  Field geologists always carry a hardness box in work.  Do you want to get one, in a Do-It-Yourself way?

This is how you can gather all the nine minerals (except diamond; you certainly do not need diamond in the field) of the hardness box, from talc, the softest, to corundum, the nearly hardest.  Some common minerals are found in countryside, while others in the urban area!  Here they are:

In countryside


QUARTZ (H. 7) is easily obtained from quartz veins elsewhere in HK.

FELDSPAR (H. 6) can be located at pegmatite, which can be seen in some abandoned quarries.  Beware of falling stones.

CALCITE (H. 3) can be collected at two places: near the old mine at Ma On Shan and Ap Chau where the conglomerate is concreted by calcite.

There are a few FLUORITE (H. 4) veins in HK.  But the best location to pick is still Ma On Shan area.

In urban area


TALC (H. 1) and GYPSUM (H. 2) are two traditional Chinese medicines.  Spend a few dollars and you can get much from Chinese herb/medicine shops.  Cut a small piece from each for the hardness box.  The rest of talc can be ground down to baby powder and use the gypsum to make bean curd, or any cake you like.

APATITE (H. 5), TOPAZ (H. 8) AND CORUNDUM (H. 9) are common gemstones.  What we require in the hardness box is not that of gem quality.  Therefore you need not buy (and certainly not to rob or steal) beautiful and expensive gem from jewelry shops.  HK holds three very large jewelry exhibitions annually (March, June and September) in which some gemstone dealers selling minerals and crystals including these three kinds.  Just select the minerals of suitable size and not necessarily with good crystal forms, and don’t forget to bargain the price.

Put all your 9 minerals in a box with dividers which can house individual minerals in separate compartments.  Add a metal nail and a copper coin to enhance the effectiveness of the hardness test.  Also try to get a magnet and a piece of white unglazed porcelain as a streak plate.  Then you will have a simple and useful tool kit for field work.

Prepared by CH Chow      updated 20101018


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