I cannot fix the names and structures of the seven crystal systems in my head. There's a thousand books explaining their geometry and it's totally fine and understandable, no problem. But what do the names mean?
- Rhombohedral or Trigonal
OK, cubic is simple enough, hexagonal too. I know that "-eder/-hedral" means "side" and "-gon" means "angle". Why is a system with three different edges and angles triclinic? What are the rationales behind each of the names?
A rhombus has sides of equal length. Orthorhombic has only right angles (orthogonal), but the sides a,b,c have different lenghts. So why "rhombic"?