How many cleavage planes do the minerals shown in the image below have?

Question

BlackTom AI · Accepted Answer

Mica minerals have one perfect cleavage plane (the basal plane), so the correct answer is 1.

1) Relevant knowledge points and concepts
- Cleavage is the tendency of a mineral to break along specific, planar directions determined by weaker atomic bonding. 
- The number of cleavage planes equals the number of distinct sets of parallel smooth surfaces produced when a mineral breaks. 
- Common examples: mica (one perfect basal cleavage), feldspar (two cleavages at ~90°), calcite (three cleavages not at 90°), halite (three at 90°), quartz (no true cleavage; conchoidal fracture).

2) Step-by-step reasoning using the image
- Observe the pieces in the photo: they form very thin, sheet-like flakes that peel off in single layers. The broken surfaces are flat and parallel across each flake.
- These features indicate one dominant plane of weakness: the mineral splits readily parallel to that plane into thin sheets.
- Count distinct orientations of smooth planar surfaces: only one orientation is visible (all sheets peel in the same direction), so there is one cleavage direction.

3) Intermediate observations (visual “calculations”)
- If there were two cleavages, we would see angular prisms or platelets with two intersecting flat directions (not present).
- If there were three cleavages, we would see blocky fragments with three intersecting sets of faces (not present).
- If there were zero cleavage, fracture would be irregular or conchoidal (curved surfaces), but the pieces are flat and layered.

4) Why the correct answer is correct
- The picture shows typical mica-like basal cleavage: very perfect, parallel, producing thin sheets — that is exactly one cleavage plane.

5) Why the other options are incorrect
- 0: rejects cleavage, but the smooth parallel sheets contradict a "no cleavage" (conchoidal) diagnosis.
- 2: would show two distinct directions of flat breakage (e.g., some feldspars) — not observed.
- 3: would produce blocky fragments with three intersecting cleavage sets (e.g., halite, calcite) — not observed.

Conclusion: The specimen exhibits one cleavage plane; the correct answer is 1.

How many cleavage planes do the minerals shown in the image below have?Single choice

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