During a mapping exercise, a geology student examined a sedimentary outcrop and recorded the following in their notes: “The well-rounded grains must be mica, since minerals with perfect cleavage are the most durable during transport. The fine clay beds here likely formed when quartz broke down under burial conditions.” When reviewing the notes, the supervising geologist questioned the accuracy of this interpretation. Which correction most accurately addresses the flawed logic in the student’s interpretation?
Answer
A
Quartz does not commonly break down into clay, and cleavage is not a reliable indicator of transport durability.
B
Mica’s cleavage makes it resistant to abrasion, so it often persists as rounded grains far from its source.
C
Minerals with perfect cleavage always remain intact, and quartz always turns into clay when buried.
D
The student’s explanation is entirely correct, and no further evidence is required to support it.
Explanation
Quartz is resistant to chemical weathering and does not commonly break down into clay; clay minerals more often form through alteration of minerals such as feldspar. Also, perfect cleavage creates planes where a mineral can split, so it does not show that the mineral will withstand transport abrasion. Choice D correctly identifies both flaws in the student’s reasoning.
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