Chris Tucker Minerals and Gemstones
Specializing in minerals and gemstones from Montana

The Summit Mine, part 2

The Minerals

Colorless crystals of aragonite are fairly common and widespread throughout the mine.  The crystals rarely exceed 1cm in length.

Pale tufts of aurichalcite have been found with wulfenite and hemimorphite in a narrow fracture about half way to the bottom of the mine.  The aurichalcite crystals reach a few millimeters in size.

Aurichalcite, 2 mm across.

Massive white barite is locally present; the barite is coarsely crystalline and occasionally forms the matrix of specimens.

Calcite is widespread throughout the mine.  Colorless to white calcite crystals can be found lining vugs and fractures.  Calcite is commonly the last mineral to have formed.

Colorless to grey cerussite crystals to 6cm have been found in localized areas.  The crystals are generally crude and rounded although sharp colorless microcrystals have been found.

Cerussite, 3 mm across.

A single chalcopyrite crystal was found in massive galena. 

Crude crystals of yellow-green chlorargyrite have been recovered from the lower reaches of the mine.  The crystals rarely exceed 4mm and generally have a "melted" appearance.  Chlorargyrite has been found with both residual sulfides and hemimorphite.

Chlorargyrite with hemimorphite, 4 mm across.

Descloizite occurs throughout the mine and is locally plentiful.  The crystals are generally sharp and vary in color from red to green to black, larger crystals tend to be distorted.  Sharp rosettes of blood-red descloizite make striking specimens.

Descloizite crystals, the largest is 2mm long.

Descloizite, 9 cm across.

Fluorite is rarely found and is one of the earliest minerals to have formed and is always massive.  In the back of one small stope several tons of massive purple fluorite occurs with secondary copper minerals.

Galena has been found as residual pieces and occasionally forms the matrix for secondary lead minerals.

Historic documents report a small quantity of gold being present in the ore.  Likely, if a sizable ore sample was to be crushed and panned, free gold would be obtained.

The Summit mine has produced some of the finest hemimorphite in the United States.  Lustrous crystals which vary from colorless to snow white and rarely a faint blue reach 12 cm in length and 6 cm across the termination.  Often forming attractive groups from thumbnails to cabinet specimens 20 cm across, occasionally associated with several other secondary silver, lead, copper, and zinc minerals.  The larger hemimorphite crystals are simple and have a chisel like habit while the smaller microcrystals tend to be more complex.  Fan shaped groups and divergent clusters, so common for the species, are abundant. 

Hemimorphite, 7 cm across.

Hemimorphite, 20 cm across.

Hemimorphite on quartz epimorphs of an unknown mineral, 6 cm across.

Hemimorphite with calcite, 14 cm across.

Hemimorphite with calcite, 12.5 cm across.

Much powdery white material is found with hemimorphite, it is believed to be hydrozincite but its identity has not been confirmed.

Microcrystals of mimetite are common, often occurring as simple elongated hexagonal prisms with a multitude of pyramidal faces in shades of yellow.  When found with wulfenite, the mimetite is often red to red-orange in color and forms globular rounded crystal groups.  White crystals have been found along with yellow crystals with a white core.  A single specimen has been found with mimetite forming crude pseudomorphs of cerussite.   

Mimetite pseudomorphs of cerussite with calcite, 1 cm across.

Mimetite, 11.5 cm.

Mimetite on wulfenite, 2 mm.

Mimetite, 6 mm across.

Pale green crystals of mottramite have been found growing on large blocky dark red descloizite crystals from one isolated area of the mine.

Mottramite on descloizite, 9 cm.

Sharp microcrystals of plattnerite are often found growing on other lead minerals.  The plattnerite crystals are often lustrous and rarely exhibit twinning.

Plattnerite with hemimorphite, largest hemimorphite is 2 mm long.

Rare massive pyrite has been encountered in the underground workings.

Quartz occurs throughout the mine and is a common cavity lining.  Quartz also frequently forms both pseudomorph of hemimorphite and epimorphs of several other minerals including calcite, descloizite, hemimorphite, cerussite, and possibly smithsonite and polybasite.  Quartz is also found in epitactic growth with hemimorphite; the Summit is one of the localities in the world where such a relationship is known to occur. 

Quartz epimorph of hemimorphite, 4 cm.

Quartz epitactic on hemimorphite, 3.3 cm tall.

Rosasite is locally plentiful in the mine.  Often the rosasite occurs as simple rounded balls that reach as 1 cm across.  More rarely coarsely crystalline rosasite microcrystals are found forming small groups, the Summit mine is one of the few localities in the world where individual rosasite crystals can be found.  Hemimorphite is often encountered with rosasite.

Acicular rosasite microcrystals, 1 mm across.

Thick blocky rosasite microcrystals, 3 mm across.

A single collector references scorodite from the mine, its occurrence can not be verified and is presence is suspect.

Smithsonite was one of the major ore minerals at the mine.  The smithsonite is commonly the massive dry bone variety.  Likely some of the "calcite" in the mine is, in part, smithsonite.

Near the lower reaches of the mine sphalerite has been found in massive galena.

Dull red-orange vanadinite is sparingly present.  The crystals are generally simple elongated hexagonal prisms.

Willemite has been found as colorless microcrystals in dump material.  Willemite has not been found in situ and its presence must be considered suspect.

Wulfenite is uncommon in the mine, although locally plentiful areas have been found.  Thin transparent yellow-orange tabular crystals to 5 mm occur sparingly throughout the mine. In the near surface workings, a single narrow fracture was encountered that contained microcrystals of tabular yellow wulfenite in association with vivid red descloizite and dull yellow mimetite. One small mineralized area produced several transparent tabular crystals of wulfenite with slight pyramidal faces, the largest being 2 cm. Frequently crystals of wulfenite have microcrystals of plattnerite growing almost exclusively on the pedion. In the lower portion of the mine a single pocket was encountered that contained hemimorphite crystals to 4 cm. Scattered about the hemimorphite were several blocky pseudocubic orange wulfenite crystals to 8 mm. Although the pocket was small, the few specimens that it produced are striking and give promise to future discoveries.

Wulfenite with calcite on quartz, 7.2 cm.

Wulfenite on quartz, 7 cm across.




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