日本語版

Is a snow crystal really one flat plate?

A single frontal photograph collapses the c-axis direction. This inquiry uses a focus-shift sequence to determine which branches become sharp at the same depth, then compares the inferred plate arrangement with an interactive 3D model.

The central question

Can a crystal that looks like an ordinary six-branched snow crystal actually contain two or more crystal plates?

Natural specimens include combined six-branched crystals, in which plates with fewer than six developed branches complement one another, and stacked forms in which complete plates overlap along the c-axis.

STEP 1

Predict from a photograph

Before watching the video, inspect branch shape, thickness, roots and overlap. Decide whether all six branches appear to belong to one plate.

  • Do all branches have the same texture and width?
  • Do their roots continue from one common centre?
  • Are there hints of different focus or overlap?
Natural combined six-branched snow crystal made of two three-branched plates at different depths
From the frontal image alone, the six branches can look coplanar.撮影・著作：© Atsushi Muta / Muta Laboratory
STEP 2

Choose an observation that can reveal depth

Move the focal plane from the front of the specimen toward the back. Branches that become sharp at the same focal position are likely to belong to the same plate or a nearby depth.

STEP 3

Watch the focus-shift specimens

The Japanese specimen collection contains two 2+4 specimens, a 1+5 combined crystal, a double six-branched crystal, a three-layer crystal and a twelve-branched form. A 3+3 arrangement remains available as an interactive 3D structural example.

Open the focus-shift video collectionStart with the P2256070 2+4 specimen
STEP 4

Assign branches to layers

Record which branches become sharp in the front, middle and back focal positions. In the P2256070 specimen, two opposite branches sharpen together at one focal plane and four other branches sharpen at another, supporting a 2+4 interpretation.

Observation and interpretation are different: focus changes show a depth relation, but they do not by themselves determine the complete formation history.
STEP 5

Verify the inferred arrangement in 3D

Rotate the model to top, oblique and side views, then separate the plates. The model organises the observed geometry; it is not a complete reconstruction of every microscopic detail.

Open the English interactive 3D models

Do not explain every unusual branch count by stacking

Five-, seven- and eight-branched appearances can also arise from unequal growth, angular splitting, missing development or damage. The Japanese morphology gateway separates these questions from the depth inquiry.

Open the branch-count and morphology inquiry (Japanese)

Atsushi Muta (2026), “The development of video teaching materials illustrating the shape of snow crystals in the thickness direction,” Journal of the Physics Education Society of Japan, 74(1), 8–11.

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