Specific Gravity

Measure of

Density

Specific Gravity is a measure of the density of a mineral. It is a useful property that sometimes becomes the only way to distinguish some minerals without laboratory or optical techniques.

Specific Gravity is the heaviness of a substance compared to that of water, and it is expressed without units. In the metric system specific gravity is the same as in the English system. If something is 7.85 times as heavy as an equal volume of water (such as iron is) its specific gravity is 7.85. Its density is 7.85 grams per cubic centimeter, or 7.85 kilograms per liter, or 7.85 metric tons per cubic meter.

Since the gram was defined as the mass of a cubic centimeter of water, water must by definition have a density of 1 gram per cubic centimeter. It actually varies a little with changes in temperature, but its density is exactly 1 somewhere around 3 or 4 Celsius degrees above freezing.

Gold can easily be distinguished from "fool's gold" by specific gravity alone, although there are many other ways. Specific gravity is a measure without units, because it is derived from the density of the mineral divided by the density of water and thus all units cancel. However, since water's density equals 1 gram per cubic centimeter (at specific conditions), then a mineral's specific gravity would also correspond to a mineral's density as expressed in grams per cubic centimeter.

Specific gravity (SG) as already stated compares the density of a mineral to the density of water. If a mineral has a SG of 2, then it is twice as dense as water. If a mineral has a SG of 3 then it is three times as dense as water and so forth. However, comparing a mineral to water is not practical and is not really helpful. It is easier to consider what is the SG of a typical mineral and compare minerals that way.

The Earth's crust is composed mostly of the minerals quartz, calcite and feldspar. These minerals have SG's around 2.75 which is close to the average SG of the rocks on the outer surface of the Earth's crust. Therefore, the SG of most rocks that people would pick up and be familiar with, will have a specific gravity of approximately 2.75.

To use specific gravity, hold a mineral of unknown SG in one hand and in the other hand a mineral of known SG preferably one near the average of 2.75 and of the same size as the unknown mineral; then compare". How does the unknown mineral compare? By convention, comparisons of SG are split between luster categories: non-metallic and metallic. Non-metallic minerals tend to be of a low density and we naturally expect them to be so. So, when one is surprisingly heavy, it becomes very diagnostic.

Measure SG

Specific gravity can be measured accurately by use of sensitive laboratory equipment. For the average rockhound a good estimate of SG can be obtained by use of a rigged balance system.

1. Weigh the mineral dry. Dry weight = D

2. Then weighed the mineral immersed in a liquid, usually water. Wet weight = W

3. Now the SG can be obtained by the following formula:

SG = D/([D-W]L)

Where L is the density of the liquid, if water is used, L=1 so that the formula is simply D/(D-W).

The mineral being tested must be homogenous and not contain other minerals. It is best to test single small crystals that are not attached to a host rock.

Units of Weight 

Units Of Measure Conversions

Gold Nuggets

For Sale Notice!

Buyer Be Ware!

Gold nuggets being sold online are sometimes sold buy intended confusing, misleading methods, and, sometimes not real naturally formed gold nuggets discovered in the Earth!

Advertisers that do not provide accurate measurements (weight & size) in certified world standard gold-market trade "troy ounce", and do not provide images of the gold nugget along with a size scale in the image, should be avoided!  No Excuses, No Exceptions!

Advertisers that present their gold nuggets with the weight presented in grns are to be watched carefully!    GRNS is the abbreviation for GRAINS not grams!   This is mostly used to mislead the average consumer, or is used by an inexperienced person.   As a buyer of gold, you must know how to do the math and know the units of standard measure for the world gold market.

• Pure Gold is Bought And Sold By Weight - The World Gold Market Standard Unit Of Weight Is The "Troy Ounce".  When you hear a market price for gold, that is the price of 1 troy ounce of pure bullion gold.   Make sure you know the troy ounce!

• There Are 480 Grains In 1 ounce (oz.).

• A GRAIN is only .0648 of a GRAM, or .0021 of an ounce.

Example:

Here's an example from an actual auction on Ebay.

A 43.1 grain gold nugget, that was manmade, sold for $112!   An Artificially made gold nugget is not that impressive to own, do to the simple fact anyone can do this!  Now Let Us Figure Out What This Nugget Was Worth AS Just Pure Gold (if it even was pure gold to begin with).

A) Do the unit-of-weight conversion math to get the actual gold standard troy ounce weight:

43.1 grains is 2.8 grams is .09 of a troy ounce!

B) Calculate the paid auction price by the price of 1 once of gold.

$112 for .09 of a troy ounce was paid.

Therefore, 1 ounce divided by .09 = 11.11.

$112 X 11.11 = $1,244 USD an ounce (troy ounce)!!!!

C) Calculate the price paid by the gram.

1 troy ounce = 31grams.

$1,244 divided by 31 grams = $40 a gram.

That's a lot of money for a 2.8 gram man-made nugget in my opinion!

A 1 gram nugget is only .032 of an ounce and the size of a match head. Not very impressive!

Bottom Line

What Is The Value Of The Specific Gold Nugget To You?

Some folks just like to collect different types of nuggets as natural nuggets or to have a One-of-a-kind jewelry piece made of it.   If you like the nugget, and the seller has given you enough honest information for you to make an informed decision, and you feel good about the price, then you have invested in a rare piece of what Nature have created - A One of a kind rare creation!

Gold - Weight Conversion Chart

Below is a conversion chart to help everyone figure out just what they are getting.  Following these self discipline rules may save you from feeling bad about a gold nugget purchase.

1. Require the seller to provide you with the weight and a current picture of the gold nugget; do not except anything less.

2. Be careful of whether the ad is advertising a nugget in grains or grams.

3. Be careful of the wording used by the seller to describe the gold nugget; note whether it is a REAL NATURAL GOLD nugget, (a natural nugget, one dug from the ground), or a REAL GOLD nugget; a nugget someone made from real gold.  A REAL NATURAL NUGGET, one that is made by Mother Nature and dug from the ground, is more valuable as a rare prized possession.

Accuracy: 4 decimal places. oz = ounce. av = average.

DWT 

DWT = Penny Weight.  This is a convenient way to size nuggets in U.S.A. because 20 pennyweights equal 1 troy ounce.

• 20 pennyweights equal 1 troy ounce.

Example: 5 dwt is a 1/4 ounce, 10 dwt is a 1/2 ounce etc.

Grams

Grams seems to be the most widely used weight measurement amongst gold nugget sellers today. Keep in mind that there are 31 grams to 1 ounce.

Example: an 8 gram nugget is a little over a 1/4 ounce, a 16 gram nugget is over a 1/2 ounce.

The Specific Gravity Test

GOLD

Use the following method to find the gold content of a gold nugget.

We will use a gold nugget that is mixed with quartz as a working example to demonstrate the testing method.

Simply put, the formula is 3.1 x the nugget's weight in water, minus 1.9 x the nugget's dry weight in air.

• Dry nugget weighs 96 grams x 1.9 = 182.4 SG

• While immersed in water, the nugget weighs 74.5 grams x 3.1 = 230.95 SG

• 230.95 - 182.4 = 48.55 SG

• 31.1 = number of grams in 1 troy ounce.

48.55SG / 31.1g = 1.56 oz. (ounces) of gold in nugget. (SG converted to ounces)

Step 1) Convert measured gram weight into ounces. Original dry weight = 96 grams / 31.1 = 3.08 ounces.

Step 2) Subtract the difference between the wet and the dry weights:
    3.08 ounces - 1.56 ounces = 1.52 ounces.

Therefore what is left is 1.52 ounces of quartz.

"Wet" = weight in water - tar out the scale, then hang nugget in water for weight if the scale will tar. Or, weigh the nugget in and out of water and subtract the difference.

The specific gravity for gold is 19.3.
The specific gravity for quartz is 2.65.
The ratio between gold and quartz is 7.28 X.