Hexagonal

6/m 2/m 2/m (D6h)

Cuatro ejes: tres horizontales iguales a 120 grados, uno vertical (a1 = a2 = a3 ≠ c)

El sistema cristalino hexagonal tiene cuatro ejes cristalográficos: tres ejes horizontales iguales que se cruzan a 120 grados y un eje vertical de longitud diferente. Los cristales suelen mostrar prismas y pirámides hexagonales. Ejemplos incluyen berilo (esmeralda, aguamarina), apatito y grafito.

The hexagonal crystal system features four axes — three equal axes in a plane at 120° to each other, plus one unique axis perpendicular to them. This six-fold symmetry produces the characteristic hexagonal prisms and bipyramids seen in many well-known minerals. The hexagonal system is home to some of the most valuable gemstones on Earth, including beryl (emerald, aquamarine) and corundum (ruby, sapphire).

Symmetry

Hexagonal crystals have a principal six-fold rotation axis (a₁ = a₂ = a₃ ≠ c, with a-axes at 120°). Looking down the c-axis, the crystal appears to have six-fold symmetry. The system contains 7 crystal classes, from the fully symmetric dihexagonal dipyramidal class to the less symmetric hexagonal pyramidal class. The Miller-Bravais index system uses four indices (hkil) rather than three, where i = -(h+k), reflecting the three equivalent a-axes. This system is sometimes confused with the trigonal system, which has three-fold rather than six-fold symmetry and is treated as a subdivision by some crystallographers.

Minerales notables

Beryl is the signature hexagonal mineral, forming the prismatic hexagonal crystals that yield emerald (green, chromium-colored), aquamarine (blue), morganite (pink), and heliodor (yellow). The largest single crystal ever found — an 18-meter beryl from Madagascar — crystallized in this system. Apatite, the mineral that forms our bones and teeth, is hexagonal and occurs in a remarkable range of colors. Molybdenite (MoS₂), the chief ore of molybdenum, forms distinctive hexagonal plates with a metallic luster. Ice itself crystallizes in the hexagonal system, explaining the six-fold symmetry of snowflakes.

Minerales (2)

Beryl (Emerald)

Be3Al2(SiO3)6

09 Silicates

Apatite

Ca5(PO4)3(F,Cl,OH)

08 Phosphates, Arsenates, and Vanadates

Preguntas frecuentes

What is the Hexagonal crystal system?
El sistema cristalino hexagonal tiene cuatro ejes cristalográficos: tres ejes horizontales iguales que se cruzan a 120 grados y un eje vertical de longitud diferente. Los cristales suelen mostrar prismas y pirámides hexagonales. Ejemplos incluyen berilo (esmeralda, aguamarina), apatito y grafito.
What minerals crystallize in the Hexagonal system?
There are 2 minerals that crystallize in the Hexagonal crystal system on MineralFYI.
What symmetry does the Hexagonal system have?
The Hexagonal crystal system has 6/m 2/m 2/m (D6h) symmetry.
What are the axes of the Hexagonal crystal system?
The Hexagonal system is characterized by Cuatro ejes: tres horizontales iguales a 120 grados, uno vertical (a1 = a2 = a3 ≠ c).