New Mexico Mineral Symposium — Abstracts

Minerals form when specific temperatures and pressures are applied to chemical solutions in a particular geologic environment, whether it be sedimentary, igneous, or metamorphic. Pseudomorphs result when the presumably stable environment of formation becomes unstable, altering the conditions, thus resulting in a new environment. Different conditions can cause instability, which produce pseudomorphs by various means. The manners in which pseudomorphs occur include
replacement or substitution; chemical alteration; and encrustation, dissolution, and resulting casts. The end result of each situation is the retention of the form of the original mineral with a partial or complete chemical alteration.

The introduction of highly silicious solutions and subsequent replacement of a fallen tree alters the original nature of the tree resulting in petrified wood, typical of Petrified Forest in northeastern Arizona. Thus, quartz is a pseudomorph after wood by replacement or substitution of the latter by the former. Quartz, in fact, is a common pseudomorphic replacement of many minerals including anhydrite, calcite, and hemimorphite, all of which occur in Arizona. The replacement is complete so that none of the original material remains.

Chemical alteration may not be so complete, as many times a core of the original minerals remains. It involves a partial addition or substraction of elements or compounds in the original mineral but still produces what can be called a pseudomorph. Add carbon, oxygen, and hydrogen to cuprite, Cu₂O, and what results is a malachite, Cu²⁺₂CO₃(OH)₂, pseudomorph after cuprite. Take away copper, carbon, and oxygen from azurite, Cu³⁺₂(CO₃)₂(OH)₂, and there is still a malachite pseudomorph, this time after azurite.

The third possibility is an encrustation of one mineral over another. Although some may call simple coatings a pseudomorph, the purist would require the complete removal of the mineral after the encrustation, leaving behind only a cast of the original.

There are examples of each of these types of pseudomorphs within the boundaries of the state of Arizona. Some of the classic and unmistakable pseudomorph occurrences include malachite pseudomorphs after azurite from Ajo and Bisbee; and Camp Verde calcite pseudomorphs after glauberite, some of which have been penetrated by post-mining chrysocolla and malachite. Other easily recognized pseudomorphs are the Bloody Basin and Inspiration malachite pseudomorphs after azurite with drusy quartz coatings. There are also Arizona localities that have produced a variety of pseudomorphs including Tiger (malachite after azurite, sauconite after cerussite), the 79 Mine (chrysocolla after hemimorphite and wulfenite), and the Flux Mine (anglesite after cerussite and cerussite after anglesite).

Localities

BISBEE
MALACHITE Cu₂CO₃(OH)₂
after AZURITE Cu₃(CO₃)2(OH)₂

 MALACHITE Cu₂CO₃(OH)₂
after CUPRITE Cu₂O

 79 MINE
CHRYSOCOLLA (Cu,Al)₂H₂Si₂O₅(OH₄)•nH₂O
after HEMIMORPHITE Zn₄Si₂O₇(OH)₂•H₂O

CHRYSOCOLLA (Cu,Al)₂H₂Si₂O₅(OH₄)•nH₂O
after WULFENITE PbMoO₄

AURICHALCITE (Zn,Cu)5(CO3)2(OH)6
after WULFENITE PbMoO

INSPIRATION
CHRYSOCOLLA(Cu,Al)₂H₂Si₂O₅(OH₄)
after AZURITE Cu₃(CO₃)2(OH)₂

TIGER
MALACHITE Cu₂CO₃(OH)₂
after AZURITE Cu₃(CO₃)2(OH)₂

SAUCONITE Na0₃Zn₃(Si,Al)₄O₁₀(OH)₂.4H₂O
after CERUSSITE PbCO₃

CAMP VERDE
CALCITE CaCO₃
after GLAUBERITE Na₂Ca(SO₄)₂

AJO
MALACHITE Cu₂CO₃(OH)₂
after AZURITE Cu3(CO3)2(OH)2

BLOODY BASIN
MALACHITE Cu₂CO₃(OH)₂
after AZURITE CCu₃(CO₃)2(OH)₂

References:

1. American Geological Institute, 1962, Dictionary of Geologial Terms.
2. Bates, Robert L. and Julia A. Jackson, 1987, Glossary of Geology: American Geological Institute.
3. Bideaux, Richard, 1980, Famous mineral localities: Tiger, Arizona: The Mineralogical Record, v. 11, pp. 159-179.
4. Graeme, Richard W., 1981, Famous mineral localities: Bisbee, Arizona: The Mineralogical Record, v. 12, no. 5.
5. Hurlbut, Cornelius and Klein, Cornelis, 1993, Manual of Mineralogy, 21st Edition: Wiley, New York.
6. Keith, Stanley B., 1972, Mineralogy and Paragenesis of the 79 Mine Pb-Zn-Cu Deposit: The Mineralogical Record, v. 3, pp. 247-272.
7. Kraus, Edward H., Hunt, Walter F. and Ramsdell, Lewis S., 1951, Mineralogy: An introduction to the study of minerals and crystals: McGraw-Hill, New York.
8. Robinson, George W., 1994, Minerals: An illustrated exploration of the dynamic world of minerals and their properties: Simon & Schuster, New York.
9. Sinkankas, J., 1964, Mineralogy: Van Nostrand Reinhold, New York.
10. Thomas, W. J. and Gibbs, R. B., 1983, Famous Mineral Localities: The new Cornelia mine, Ajo, Arizona: The Mineralogical Record, v. 14, pp. 85-90.
11. Thompson, J. R., 1983, Camp Verde evaporites: The Mineralogical Record, v. 14, pp. 85-90.
12. Thompson, W., 1980, Chrysocolla pseudomorphs from Ray, Arizona: The Mineralogical Record, v. 11, pp. 248-250.