A true macle, as I was was taught, is a twinned crystal. I
understand what a twinned crystal is, but I've never grasped how a
macle IS that - I for one would be happy if someone could explain
that in clear terms......
Few preliminaries before tackling macle question.
Cube shaped crystals do exist. However, they are so rare that the
crystal itself is more valuable than a diamond faceted from it. I do
not believe they are used to cut diamonds from.
Two commonest crystal forms are octahedron, aka “indian type” and
dodecahedron aka “brazilian type”. Cleavage is always parallel to a
pair of octahedral faces. Since octahedron have 4 such pairs, there
are 4 cleavage directions.
To understand macle, which is a octahedral crystal, half of each was
twisted alongside cleavage plain by 180 degrees, do the following:
take some play dough and fashion an octahedron out of it. with a
knife or a wire separate your octahedron in two parts - separation
line been parallel to any pair pair of parallel octahedral faces.
take one separated part and rotate it 180 degrees. stick both parts
together again and you have your macle.