Hexagonal

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

4軸：120度で交わる等長水平3軸と垂直1軸 (a1 = a2 = a3 ≠ c)

六方晶系は4本の結晶軸を持ちます。120度で交わる等長の水平3軸と、それとは長さの異なる垂直1軸で構成されます。結晶はしばしば六角柱や六角錐の形態を示します。代表例にはベリル（エメラルド、アクアマリン）、燐灰石、黒鉛などがあります。

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.

注目の鉱物

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.

鉱物 (2)

Beryl (Emerald)

Be3Al2(SiO3)6

09 Silicates

Apatite

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

08 Phosphates, Arsenates, and Vanadates

よくある質問

What is the Hexagonal crystal system?
六方晶系は4本の結晶軸を持ちます。120度で交わる等長の水平3軸と、それとは長さの異なる垂直1軸で構成されます。結晶はしばしば六角柱や六角錐の形態を示します。代表例にはベリル（エメラルド、アクアマリン）、燐灰石、黒鉛などがあります。
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 4軸：120度で交わる等長水平3軸と垂直1軸 (a1 = a2 = a3 ≠ c).