Stone Science
Glossary
A quick-reference list of scientific terms used across the Stone Science section.
Key terms
Short definitions (expanded pages provide context and examples).
Aphanitic / phaneritic
Fine-grained (crystals too small to see) vs. coarse-grained (crystals visible).
Clastic
Made of fragments (clasts) of pre-existing rocks/minerals (common in siliciclastic sedimentary rocks).
Cementation
Minerals precipitate between grains and bind sediment into rock (diagenesis).
Felsic / mafic
Silica-rich, light-colored vs. Mg-Fe rich, dark-colored (igneous composition terms).
Index mineral
A mineral that indicates metamorphic conditions (temperature/pressure) and grade.
More terms
Common words you’ll see in scientific rock descriptions.
Foliation
Planar fabric in metamorphic rocks caused by aligned minerals or compositional banding.
Lithification
Turning sediment into rock through compaction + cementation.
Porphyritic
Large crystals (phenocrysts) set in a finer groundmass—two-stage cooling history.
Protolith
The original rock before metamorphism.
Streak
Powder color of a mineral on unglazed porcelain; often diagnostic.
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