Specific Gravity Testing

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Overview

Specific gravity (SG) measures a gemstone's density relative to water. It's a non-destructive test that helps identify gems and detect treatments.

How It Works

Using Archimedes' principle, the gem is weighed in air and then suspended in water. The difference in weight determines the volume displaced, allowing calculation of density.

Equipment Needed

  • Precision balance (0.01g accuracy)
  • Beaker with distilled water
  • Wire basket or gem holder
  • Thermometer

Procedure

  1. Weigh the gem in air (W_air)
  2. Suspend the gem in water using a wire basket
  3. Record the weight in water (W_water)
  4. Calculate SG = W_air / (W_air - W_water)
  5. Adjust for water temperature if needed

Typical Values / Results

Gemstone Value / Observation
Diamond 3.52
Ruby/Sapphire 4.00
Emerald 2.72
Quartz 2.65
Topaz 3.53

Limitations

Small stones are difficult to measure accurately. Porous gems may absorb water, affecting results. Included gems may have variable SG.