Why Snow Crystals Grow Six Arms
Written by Studio AM.
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A snow crystal can begin when water vapor forms ice around a tiny particle in a cloud. Water molecules join the growing ice in an orderly pattern. That pattern has sixfold symmetry, so a flat crystal often develops six corners or arms.
The arms grow through nearly the same cloud at the same time. They therefore meet similar temperature and moisture conditions. Each arm may develop similar ridges or branches. The shapes grow independently under similar conditions.
Conditions change as the crystal falls. A slightly wetter layer can encourage branching, while another temperature can favor flat plates. When six clear arms develop, they can resemble one another because they share the journey. Many snow crystals are irregular instead. No two crystals need follow exactly the same path, so their fine details can differ.
Sixfold structure comes from molecular arrangement; elaborate decoration comes from changing growth conditions. A snowflake records both an invisible rule inside ice and a visible history of its trip through a cloud.
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Questions
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Question 1 of 4
What is the main idea of the passage?
The answer is A: Water’s sixfold ice structure and shared changing cloud conditions shape a snow crystal’s six similar arms.
The passage distinguishes the molecular source of six arms from the environmental source of detailed branches.
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Question 2 of 4
Why do the six arms often develop similar details?
The answer is B: They travel together through nearly the same sequence of conditions.
Shared temperature and moisture provide similar growth opportunities at the same time.
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Question 3 of 4
What does “symmetry” mean here?
The answer is C: a balanced pattern repeating around a center
The crystal’s molecular pattern repeats into six corresponding corners or arms.
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Question 4 of 4
What may a wetter cloud layer encourage?
The answer is D: branching
The third paragraph says a slightly wetter layer can encourage branching.
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