Hexagonal

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

四轴：三条等长水平轴以120度相交，加一垂直轴 (a1 = a2 = a3 ≠ c)

六方晶系具有四条结晶轴：三条等长水平轴以120度相交，以及一条长度不同的垂直轴。晶体常呈六方柱和六方锥形态。典型矿物有绿柱石（祖母绿、海蓝宝石）、磷灰石和石墨等。

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.

著名矿物

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.

矿物 (2)

Beryl (Emerald)

Be3Al2(SiO3)6

09 Silicates

Apatite

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

08 Phosphates, Arsenates, and Vanadates

常见问题

What is the Hexagonal crystal system?
六方晶系具有四条结晶轴：三条等长水平轴以120度相交，以及一条长度不同的垂直轴。晶体常呈六方柱和六方锥形态。典型矿物有绿柱石（祖母绿、海蓝宝石）、磷灰石和石墨等。
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 四轴：三条等长水平轴以120度相交，加一垂直轴 (a1 = a2 = a3 ≠ c).