Base elements → Materials → Mineral materials

EMERALD

Table of main properties of emerald

 

Property Typical Value Remarks
Density ~2.7–2.8 g/cm³ Moderate
Young’s modulus (E) ~200–300 GPa High
Compressive strength ~1000–1500 MPa Moderate to high
Hardness (HV) ~500–800 HV Moderate
Hardness (Mohs) 7.5–8 Lower than sapphire/ruby
Thermal conductivity ~2–5 W/m·K Low
Electrical conductivity Very low Insulating material
Thermal expansion ~5–8 ×10⁻⁶ /K Low
Melting point ~1200–1400 °C Decomposes before melting
Magnetism No Non-magnetic
Corrosion resistance Good Chemically stable but sensitive to inclusions
Machinability Not machinable Cut and polished only

Emerald is a variety of beryl (Be₃Al₂Si₆O₁₈), characterized by its green color due to the presence of chromium and/or vanadium. An emblematic precious stone, it is used in watchmaking exclusively for jewelry applications.

Unlike other materials used in technical watchmaking, emerald exhibits intrinsic fragility due to the frequent presence of internal inclusions. These characteristics significantly limit its use to components that are not subjected to mechanical stress or impact.

Main Properties

Emerald exhibits the following properties:

  • Moderate hardness (7.5 to 8 on the Mohs scale)
  • Brittle crystalline structure (presence of inclusions)
  • Low impact resistance
  • Good chemical stability
  • Non-magnetic material
  • Low tensile strength
  • Excellent optical quality (transparency and color)

Natural emerald is characterized by:

  • Characteristic inclusions (known as “emerald garden”)
  • Variations in color and transparency
  • A heterogeneous internal structure

These inclusions, although aesthetically valued, constitute areas of mechanical weakness.

Although all types of cuts can be applied, emeralds are generally cut as follows:

  • Emerald cut (rectangular with truncated corners)
  • Round cut (less common)
  • Cabochon cut (depending on quality)

1. External Jewelry Components (Rare)

Due to its fragility and sensitivity to impacts, emerald is very rarely used for setting on such external components.

2. Dials (Most Common Use)

Advantages

  • Exceptional aesthetic appeal
  • Unique and recognizable color
  • High jewelry value
  • Noble material

Limitations

  • High fragility
  • Sensitivity to shocks
  • Presence of inclusions
  • Difficult implementation
  • Strictly decorative use
  • High cost