What is the term for the most common twinned diamond crystal form?

• A. Bort
• B. Esk
• C. Giras
• D. Macle

Answer: (D)

Twinned crystal forms arise when diamond crystals grow together along a twinning plane, creating mirror-image halves. The most common form you’ll see in rough diamonds is called a macle. A macle is typically two (or more) octahedral crystal segments that have grown together along a twinning plane, so you get a paired, intergrown shape with a visible seam. This is a classic and widely recognized twinned form in diamonds, which is why it’s the correct term. The other terms are not used to describe this specific crystal habit; for example, bort refers to rough, lower-quality material, and esk or giras aren’t standard terms for diamond crystal twinning.