H5P Content 14948

Sometimes it's hard to tell whether a well-formed mineral crystal is displaying crystal habit (i.e., it grew that way), or whether it's a broken piece of a mineral with cleavage (i.e., it broke into a particular shape because of a specific pattern of weaknesses in its atomic structure).

The image shows two samples for each of two minerals. Three of the samples are pieces broken from a bigger crystal. Can you figure out which of the larger samples (A or B) is also a broken piece?

Use left and right arrow to change slide in that direction whenever canvas is selected.

Slide 1

A (top): a rounded green crystal with irregular broken fragments next to it. Bottom (B): A blocky clear crystal with box-shaped fragments next to it.

Broken pieces

Advance the slides for an explanation.

Which of the larger samples (A or B) was broken from a bigger crystal?

A. The large green crystal is the broken fragment.
B. The large clear crystal is the broken fragment.

Broken pieces

Left- a green crystal many flat faces. Right: More of the same, except as fragments with irregular edges.

A. Olivine

The crystal grew this way.

The broken olivine crystals have irregular surfaces, meaning they are displaying fracture, not cleavage. Breaking would not have resulted in the smooth faces on the large crystal, so it must have grown that way.

Broken pieces