Hardness of Minerals

In terms of reliability, hardness is one of the better physical properties for minerals. Specimens of the same mineral may vary slightly from one to another, but generally they are quite consistent. Inconsistencies occur when the specimen is impure, poorly crystallized, or actually an aggregate and not an individual crystal.

Hardness is one measure of the strength of the structure of the mineral relative to the strength of its chemical bonds. Minerals with small atoms, packed tightly together with strong covalent bonds throughout tend to be the hardest minerals. The softest minerals have metallic bonds or even weaker van der Waals bonds as important components of their structure. Hardness is generally consistent because the chemistry of minerals is generally consistent. Hardness can be tested through scratching. A scratch on a mineral is actually a groove produced by microfractures on the surface of the mineral. A mineral can only be scratched by a harder substance. A hard mineral can scratch a softer mineral, but a soft mineral can not scratch a harder mineral (no matter how hard you try). Therefore, a relative scale can be established to account

for the differences in hardness simply by seeing which mineral scratches another. That is exactly what French mineralogist Friedrich Mohs proposed almost one hundred and seventy years ago. The Mohs Hardness Scale starting with Talc at 1 and ending with Diamond at 10, is universally used around the world as a way of distinguishing minerals. Simply put; the higher the number, the

harder the mineral.

The Mohs Hardness Scale

1 Talc

2 Gypsum

3 Calcite

4 Fluorite

5 Apatite

6 Orthoclase

7 Quartz

8 Topaz

9 Corundum ( Ruby & Sapphire)

10 Diamond

Gold Facts


Melting point= 1948 degrees Fahrenheit

Specific gravity is 19.3

Hardness=2.5 on Mohs scale

How Gold Is Measured -

Gold, Silver, and other precious metals are universally bought and sold in Troy ounces. A Troy ounce is heavier than a standard ounce as there are only 12 troy ounces in a pound. Troy ounces are usually subdivided into either

Pennyweights, abbreviated (dwt), or Grams. Professional gold dealers prefer grams but pennyweights are preferred by gold prospectors.

In the pennyweight system each Troy Ounce is divided into 20 units called Pennyweights and each pennyweight is further divided into 24 grains. Therefore one troy ounce is equal to 480 grains. This is the same system used in measuring gunpowder and probably accounts for the popularity of the pennyweight system. Most of the early prospectors had no idea what a gram

was but they all had a gun powder scale that was calibrated in grains. The metric system is easy to use because all you need to remember is that one

troy ounce is 31.1 grams. Since this is based on the metric system grams are simply divided into 1/10th or 1/100th units. When you are buying or selling gold you must be careful when talking to

someone about a quantity of gold. Make sure that the ounces you are talking about are the same ounces you are thinking about. Here are a few conversions to help you keep this straight.

One Troy lb (pound)=12 troy ounces

One troy oz=20 pennyweight (dwt)

One pennyweight = 24 grains

One troy oz=480 grains

One troy oz=31.1 grams

Carat and Karat

Carat abbreviated “ct.” and spelled with a “c” is a

measure of weight used for gemstones. One carat

is equal to 1/5 of a gram (200 milligrams). Stones

are measured to the nearest hundredth of a carat. A

hundreth of a carat is also called a point. Thus a .10

carat stone can be called either 10 points, or 1/10 of

a carat. Small stones like .05, and .10ct are most

often referred to by point designations.

Karat with a “K” is a measure of the purity of a

gold alloy. Pure gold is 24 karat and 12 karat gold

is 50% gold.

24K 100% gold

18k 75% gold

14K 59% gold

12k 50% gold

Tips on digital scales

Digital scales are widely available today that are

inexpensive and very accurate. These scales can

be easily adjusted to weigh in several formats

including grams and pennyweights. If you are

using one of these scales you need to be sure that

the scale is set to use the format you prefer. Areas

of potential confusion include the way some

scales abbreviate grams and grains, and the

similarity of troy and regular ounces. Be sure you

check to see that you and your scale are on the

same page.


If you are using the gram format it is easy to do a

quick check of the format selection and the

calibration of the scale by weighing a $1.00 bill

or a nickel. The $1.00 bill should weigh almost

exactly one gram and the nickel should weigh

almost exactly five grams.