Pseudomorph
A mineral specimen retaining the recognisable external crystal shape of an earlier mineral, despite replacement or alteration of the original material.
Language and route: Scientific European term; French pseudomorphose in early mineralogy, built from Greek elements. Greek pseud- ‘false’ + morphḗ ‘form’ → French pseudomorphose → scientific English pseudomorph.
Literal gloss: false form
The name and its history
René Just Haüy (French *pseudomorphose*) · 1801, Traité de minéralogie, I, pp. 140–145 (secondary historical page attribution)
- What does the word literally mean?
- The apparent crystal form is ‘false’ because it reflects an earlier substance rather than the crystal symmetry of the material now present. This does not imply deceit, nor necessarily one mechanism of mineral replacement.
- What did the original author mean?
- Haüy's pseudomorphose (1801) referred broadly to mineral bodies whose outer shape came from other pre-existing objects, with extensive examples of mineralised shells and wood. It was not restricted to replacement of one crystalline mineral by another.
- Why was the name needed?
- His system needed vocabulary for bodies that appeared to have the shape of an object different from the material making them up.
- What evidence supported the original concept?
- Haüy's Traité de minéralogie I (1801), pp. 140–145, is the reported passage; specialist mineralogical historical literature recounts examples and meaning. This edition has linked the digitised original volume, but has not certified a complete word-for-word collation of pp. 140–145.
- How has geology changed the concept?
- The modern collector's and mineralogical use focuses on preservation of outward crystal shape after material change. Fossil casts, encrustations and replacement textures are now distinguished more carefully, although boundaries can be messy.
Further historical context
René Just Haüy used French pseudomorphoses in his Traité de minéralogie (1801, vol. I, pp. 140–145). In his account the category was much broader than modern replacement pseudomorphs: it included bodies such as mineralised shells and wood whose forms were inherited from other objects.
Modern mineralogists generally distinguish crystal-shape-preserving mineral replacement (pseudomorph) from replacements of fossils or other non-crystalline objects; coatings and hollow casts introduce the related but differently defined terms epimorph and perimorph. The historical shift is from a broad ‘misleading form’ category to a more constrained crystallographic usage.
Editorial qualification
Historic 1801 priority supported by secondary literature and location of original volume; exact French phrasing not transcribed independently. Old concept includes fossils, unlike modern narrow usage.
Related names
Epimorph · Chlorite · Tourmaline · Quartz · Fossil
Sources
- Harshbarger, historical study of pseudomorphs (Mindat) — Secondary discussion locating Haüy (1801), Traité de minéralogie I, pp. 140–145
- Mindat, Pseudomorph glossary definition — Modern mineralogical usage
- Mindat expert nomenclature discussion on epimorph/perimorph — Documented variation and historical disagreement over related terms
- Haüy (1801), Traité de minéralogie, digitised original — Digitised primary volume; reported reference I, pp. 140–145; not fully collated in this edition
- Fraizer, historical mineralogical explanation, Friends of Mineralogy (2004) — Specialist historical summary of Haüy’s originally broad sense, including fossils