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
9 Corundum ( Ruby & Sapphire)
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
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.
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