What Is Density (Specific Gravity)?
Density is defined as the amount of mass per unit of volume. In gemology, we usually refer to it as specific gravity (SG), which compares the density of the gemstone to that of water.
- Specific gravity = weight of the gemstone ÷ weight of an equal volume of water
Each gemstone has a characteristic SG range. For example:
- Diamond: approx. 3.52
- Ruby/Sapphire (corundum): approx. 4.00
- Quartz: approx. 2.65
- Zircon: approx. 4.6–4.7
Why Density Matters
1. Weight vs. Size
Two gemstones of the same carat weight can look different in size because of their density:
- A zircon will appear smaller than a quartz of the same weight, because it is denser.
- This can affect your expectations when buying a gemstone by carat.
2. Gem Identification
Gemologists use specific gravity as a reliable tool to distinguish between similar-looking stones. For example:
- Spinel and ruby can be similar in color, but they have noticeably different densities.
3. Detecting Simulants or Fakes
Gem imitations often have different densities than the genuine stones they mimic. A mismatch in SG can signal a synthetic or treated stone.
Why Density Matters for Buyers
Different types of gemstones vary widely in density – and this is especially important for consumers to understand.
Unlike diamonds, which are commonly purchased by carat weight, colored gemstones vary significantly in density. This means that buying strictly by weight can lead to unexpected size differences.
Example:
- A 1-carat sapphire is visibly smaller than a 1-carat diamond.
- A 1-carat opal is larger than both.
This is why visual appearance and millimeter dimensions are just as important as carat weight when comparing colored gems.
A Wide Range of Densities
Most gemstones are 2 to 4 times denser than water, which is the basis for specific gravity. However, the full range is broader:
- Amber has a very low SG of ~1.0
- Diamond ranges from 3.50 to 3.53 – about average
- Cinnabar can reach SG values as high as 8.0 – making it extremely dense
These variations affect how a gemstone feels in hand, how it’s set in jewelry, and how large it looks at a given carat weight.
What Should Customers Know?
- Density is not a quality grade, but a physical property that affects appearance and feel.
- Heavier stones feel denser and more compact, even when they appear smaller.
- Density is especially important when comparing similar-looking stones, or when verifying authenticity.
How We Use Density at Sosna Gems
At Sosna Gems, we consider SG when evaluating and identifying all our gemstones. If you order a certified gem, its specific gravity is tested and documented in lab reports (e.g., IGI, GIA).
We use precise digital scales and immersion techniques to determine SG when necessary – especially when verifying rare stones or identifying simulants.
Still curious?
Contact our team of gemologists with your questions. We're here to provide expert clarity and confidence behind every stone you choose.
