Which term describes a crystal distorted during growth, with two or more intergrown crystals with opposing crystal directions?

Which term describes a crystal distorted during growth, with two or more intergrown crystals with opposing crystal directions?

• A. Grain lines
• B. Habit
• C. Twinned crystal
• D. Macle

Answer: (C)

Twinning in crystals is when part of a crystal grows with a specific orientation relative to another part, creating two or more intergrown domains that have related but opposite directions. This results in a single crystal that behaves as if it’s composed of two crystals mirrored across a plane, giving that distorted appearance and the sense of opposing directions. That exact scenario fits a twinned crystal: the crystal is not just one block, but a pair (or more) of lattice arrangements linked together. In diamonds you’ll sometimes hear about a macLe, which is a classic example of twinning—two crystal segments joined along a common plane. But macLe describes a particular twinned diamond shape; the broader term for the phenomenon is twinned crystal, which is why it’s the best descriptor here. The other terms don’t capture the intergrown, oppositely oriented nature: habit refers to the usual external form of a single crystal, and grain lines describe internal growth features, not the intergrowth of distinct crystal domains.

Twinning in crystals is when part of a crystal grows with a specific orientation relative to another part, creating two or more intergrown domains that have related but opposite directions. This results in a single crystal that behaves as if it’s composed of two crystals mirrored across a plane, giving that distorted appearance and the sense of opposing directions. That exact scenario fits a twinned crystal: the crystal is not just one block, but a pair (or more) of lattice arrangements linked together.

In diamonds you’ll sometimes hear about a macLe, which is a classic example of twinning—two crystal segments joined along a common plane. But macLe describes a particular twinned diamond shape; the broader term for the phenomenon is twinned crystal, which is why it’s the best descriptor here. The other terms don’t capture the intergrown, oppositely oriented nature: habit refers to the usual external form of a single crystal, and grain lines describe internal growth features, not the intergrowth of distinct crystal domains.