5-Chapter 5 Diploma Weight, Density and Specific Gravity
Chapter 5 Diploma Weight, Density and Specific Gravity
High-density liquid can be used:
To separate mixed materials and similar-looking stones by specific gravity, allowing the efficient extraction of heavier particles from lighter ones.
To pick out the odd stones from many small specimens
to distinguish between two similar or small stones, enabling the identification of desired gemstones or minerals based on their density and physical properties.
Two organic SG liquids or heavy liquids are used for SG measurement:
di-iodomethane (SG 3.33)
1-bromonaphthalene (SG 1.49) - commonly used for lighter samples as it provides a different density measurement that complements di-iodomethane.
The liquids are used to get 3 SGs: 2.65, 3.05 and 3.33
SG = 2.65;
Start with di-iodomethane, add 1-bromonaphthalene, and add a piece of pure quartz until it freely dissolves/suspended in it.
SG = 3.05;
Same as above, but with a piece of tourmaline. Add a piece of tourmaline until it freely dissolves/suspended in it.
SG = 3.33
only di-iodomethane
Be careful: temperature and differential evaporation can influence the SG.
The hydrostatic method is a method to determine the SG of a material.
It gives accurate results except for the stones under 1 ct.
For the smaller stones, a less accurate result.
What is Archimedes’ principle:
An object totally immersed in a fluid experiences an upward force equal to the weight of the fluid it displaces.
Dividing the weight of a material by the volume of water displaced gives the density of a material
This means that the density can be calculated by comparing the weight of the object in air to its weight in water.
SG measurements can be done with:
a spring balance, for larger stones
a single-pan balance which is specifically for smaller stones,