Specific Gravity Checker

Calculate specific gravity (SG) to identify gemstones by their density. SG is a key diagnostic property that helps distinguish between different gemstone families.

SG Calculator

SG = Weight in Air ÷ (Weight in Air - Weight in Water)

Archimedes' Principle - Hydrostatic Method

Weight in Air (grams)

Example: 2.35g for a typical 1ct ruby

Weight in Water (grams)

Example: 1.78g for a 2.35g ruby in water

Results

3.99

Ruby/Sapphire

Confidence: 95%

Corundum family - Natural ruby or sapphire

SG Reference Chart

Gemstone	SG Range	Category
💎 Diamond	3.52	Precious
❤️ Ruby / 💙 Sapphire	3.99 - 4.01	Corundum
💚 Emerald	2.70 - 2.78	Beryl
💛 Topaz	3.53 - 3.56	Topaz
🌈 Opal	2.15	Opal
💜 Amethyst	2.65	Quartz
💚 Peridot	3.34	Olivine
💙 Aquamarine	2.68 - 2.74	Beryl
💖 Morganite	2.80 - 2.90	Beryl
🧡 Citrine	2.65	Quartz
🤎 Smoky Quartz	2.65	Quartz
💚 Tourmaline	3.02 - 3.26	Tourmaline
💙 Zircon	4.00 - 4.70	Zircon
🤍 Moonstone	2.56 - 2.59	Feldspar
💚 Jadeite	3.30 - 3.38	Jade

SG Categories

Very Light (< 2.50)

Opal (2.15), Amber (1.08), Jet (1.30)

Light (2.50 - 3.00)

Quartz (2.65), Beryl (2.70-2.78), Turquoise (2.60-2.80), Feldspar (2.56-2.59)

Medium (3.00 - 3.50)

Diamond (3.52), Topaz (3.53-3.56), Peridot (3.34), Tourmaline (3.02-3.26)

Heavy (3.50 - 4.00)

Corundum (3.99-4.01), Garnet (3.80-4.20), Zircon (4.00-4.70)

Very Heavy (> 4.00)

Zircon (4.00-4.70), Hematite (5.00-5.30), Cassiterite (6.80-7.10)

How to Measure Specific Gravity

Step 1: Weigh in Air

Use a precision scale to weigh your gemstone in air. Record this as "Weight in Air".

Step 2: Weigh in Water

Suspend the gemstone in water using a thin wire or basket. Record as "Weight in Water".

Step 3: Calculate

Use the formula: SG = Weight in Air ÷ (Weight in Air - Weight in Water)

Step 4: Compare

Compare your result with the reference chart to identify possible gemstone types.

Frequently Asked Questions

Why is specific gravity important?

Specific gravity is a fundamental physical property that helps identify gemstones. Unlike color which can vary, SG is consistent within gemstone species and helps distinguish between visually similar stones (e.g., diamond vs. cubic zirconia).

What equipment do I need?

You need a precision scale (0.01g accuracy), a container of water, and a thin wire or basket to suspend the gemstone. Professional gemological scales often include a built-in hydrostatic weighing function.

Can I measure SG for mounted stones?

SG measurement requires the stone to be freely suspended in water. Mounted stones cannot be accurately measured using this method. For mounted stones, refractive index testing is more appropriate.

How accurate is SG testing?

With proper equipment and technique, SG can be measured to ±0.01 accuracy. This is sufficient to distinguish between most gemstone species, though some overlapping ranges exist (e.g., corundum and zircon).

What affects SG measurements?

Temperature (water density changes with temperature), air bubbles on the stone, impurities in the water, and accuracy of your scale can all affect results. Use distilled water at room temperature for best results.

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