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Does a changed rock surface prove a new mineral formed?
A rock can break into fragments without changing the chemical identity of its minerals.
Sources for this view
Mechanical weathering changes physical form; chemical weathering involves chemical change in at least some mineral material. Dissolution can move constituents into solution. A rough or pale surface is therefore a clue that needs more than a visual label.
Sources for this view
Explore the model (optional)
EXPLORE THE MODEL
Repeating planes and a diffraction condition
Inspect the structure; select a site or component for its label.
What this representation means
Illustrative plane spacing; this is not a measured mineral pattern. One angle cannot identify a mineral. Intensities, atomic basis, texture and peak widths are omitted.
- Interplane separation
- 0.3 nm
- Within-plane spacing
- Illustrative, not calibrated
- Atomic identities
- Unspecified in this geometric model
nλ = 2d sin θ; n = 1
Read sampled numerical values
| Plane spacing d (nm) | Allowed 2θ |
|---|---|
| 0.12 | 79.83 |
| 0.155 | 59.57 |
| 0.19 | 47.82 |
| 0.225 | 40.02 |
| 0.26 | 34.45 |
| 0.295 | 30.26 |
| 0.33 | 26.99 |
| 0.365 | 24.36 |
| 0.4 | 22.2 |
| 0.435 | 20.39 |
| 0.47 | 18.86 |
| 0.5 | 17.72 |
The displayed planes are separated by the chosen d. θ is the angle to a plane; instruments commonly report the scattering angle 2θ. Different structures can share a spacing, so this condition alone cannot identify a mineral.
What this model can establish
Illustrative plane spacing; this is not a measured mineral pattern. One angle cannot identify a mineral. Intensities, atomic basis, texture and peak widths are omitted.
Optional: check your understanding
MAKE THE CONNECTION
Which observation alone proves a new mineral identity?