SME
Mineralogy · Problem type
A crystal system from its axes and angles
Use this for “Zircon’s cell has a = b ≠ c with every angle 90°. Which crystal system is it?”
Sort
Which crystal system is each cell?
Tap a card, then tap its group.
Count the equal edges and the right angles: the more alike they are, the more symmetric the system.
Assumptions
•
a, b and c are the cell’s three edges; the angles are the ones between them.
•
Hexagonal and trigonal cells share a = b ≠ c with 120° between a and b; the 6-fold or 3-fold axis tells them apart.
•
A mineral keeps its system however big or oddly shaped the crystal grows.
Topic check
See what you know: 5 questions on this topic
New questions each time. Pass to mark it complete.
Related lessons
Crystallography
Main lesson
A cubic plane’s spacing and its peak
Use this for “Halite is cubic with a = 5.640 Å. Find the spacing of its (200) planes and their 2θ peak with copper Kα.”
A mineral’s density from its unit cell
Use this for “Halite (58.44 g/mol) is cubic with a = 5.640 Å and 4 NaCl units per cell. Find its density.”