a. 菱形的(菱形体的,三角晶系的)

[ adj ]
having threefold symmetry
<adj.all>

Rhombohedral \Rhom`bo*he"dral\, a. (Geom. & Crystallog.)
Related to the rhombohedron; presenting the form of a
rhombohedron, or a form derivable from a rhombohedron;
relating to a system of forms including the rhombohedron and
scalenohedron.

{Rhombohedral iron ore} (Min.) See {Hematite}.

{Rhombohedral system} (Crystallog.), a division of the
hexagonal system embracing the rhombohedron,
scalenohedron, etc.