Listed below are minerals found in the Black Hills:

(Click on any of these minerals and it will link you to some simple information about that mineral along with a photograph of a sample of the mineral.)

Almandite Grossularite  Quartz
Analcime Gypsum Rare Earth Elements
Andradite Hematite Sand & Gravel
Bentonite Lepidolite Scheelite
Beryl  Limestone Schorl
Biotite Magnetite Shale
Cassiterite Muscovite Slate
Columbite/Tantalite Plagioclase Feldspars Spessartite
Dolomite Potassium Feldspars Spodumene
Fluorapatite Pyrope Talc
Wolframite Zircon

                                                                     

    


Almandite

This mineral is one of the six that are part of the garnet group.  This mineral is predominant throughout the Black Hills since it occurs in igneous rocks along with a wide variety of metamorphosed rocks. 

This mineral is predominant in the rocks around Keystone, South Dakota.  Most of the samples are small dodecahedral crystals which are a component of the biotite-garnet-staurolite schist at the Ingersoll mine near Keystone.

 The chemical formula for this type of garnet is: Fe3Al2(SiO4)3

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Analcime

This is a picture of Analcime.

This mineral occurs predominantly with a radioactive lignite bed several inches thick in the upper member of the Tongue River Formation near Ludlow.  It was also observed in the Lonesome Pete Mine.  The habit of the crystals usually is trapezohedrons and clear and colorless in the smaller crystals while the larger ones contained a black inclusion concentrated in the center of the crystal. 

The chemical formula for this mineral is: NaAlSi2O6*H2O

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Andradite

This is another one of the six types of garnets.  The main occurrence of this variety of garnet is in Lawrence County, around the Ragged Top Mountain.  This variety has been observed as small dark-brown masses with acmite, augite, and magnetite grains in that area. 

The chemical formula for this variety of garnet is:Ca3Fe2(SiO4)3

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Bentonite

 

Bentonite is predominatly made of montmorillonitic clay, derived from alateration of volcanic ash or tuff. Bentonite is predominantly mined in the Belle Fourche area on the northern end of the Black Hills.  The beds are very widespread and abundant in beds up to several feet thick among the shales of the Upper Cretaceous Graneros and Pierre formations.  

The chemical formula for this mineral is: Al2Si4O10*nH20

 

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Beryl

This mineral occurs mainly within granite pegmatites.  This mineral was mined throughout the Black Hills and can be found at many localities.

It was mined mainly as a source of beryllium. Some of the crystals recovered were of such good quality that they were used as gems. 

The chemical formula for this mineral is: Be3Al2Si6O18

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Biotite

 

This mineral is found within the igneous rocks located throughout the Black Hills. It also appears in many of the metamorphic rocks and occurs as small grains in most of the slates and phyllites but attains its maximum importance in certain gneisses and schists.

The chemical formula for this mineral is: K(Mg,Fe)3(AlSi3O10)(OH)2

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Cassiterite

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Was found first in the northern in association with gold dust from the streams.  Later it was found in the southern Black Hills.  Cassiterite occurs in the pegmatites, albitic muscovite granites, quartz veins, contact metamorphic rocks and pacer deposits.

Most of the occurrences are scattered in size and amounts per ton of rock.  Some of the best occurrences are in Pennington County area mainly around Hill City.   The crystals that occur are usually deep-ruby, brown, black, or gray grains that range in size from 1/2 inch to 6 by 6 by 11 inches. 

The main purpose for its mining was for tin (Sn).  In recent years there has been very little activity for this mineral.

The chemical formula for this mineral is: SnO2

 

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Columbite/Tantalite

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The Black Hills have received world-wide recognition for the many excellent specimens of columbite-tantalite collected from area pegmatites.  Columbite and tantalite are end members in a solid solution series.

The chemical formula for this mineral is:

Columbite        (Fe,Mn)(Nb,Ta)2O

Tantalite        (Fe,Mn)(Ta,Nb)2O6

 
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Dolomite

Can occur with some of the gold deposits in the Black Hills, in certain marbles, and as small rhombhedrons with curved faces lining the cavities in dolomitic limestone. Most of the marble based samples came from Custer County in the southern Black Hills while the remaining occurrence with gold deposits came from the northern Black Hills in the Homestake Mine. 

The chemical formula for this mineral is: Ca(Mg,Fe,Mn)(CO3)2

 

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Fluorapatite

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This is the most common variety in the apatite series of minerals.  It is very abundant throughout the Black Hills.  It is common in all three types of rocks, sedimentary, metamorphic, and igneous. 

The chemical formula for this mineral is:  Ca5(PO4)3F

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Grossularite

This mineral is one of the six that are part of the garnet group.  This particular type of garnet is found mainly in the Pennington county area.  Most of the occurrences are around the Keystone and Hill City area.  The crystals found were pink in color and very small, less than a few millimeters in size, but in large abundances. 

The chemical formula for this mineral is:  Ca3Al2(SiO4)3

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Gypsum

Gypsum occurs in large quantities throughout the Black Hills.  It is found surrounding the Black Hills in the red beds of the Spearfish formation and massive beds overlying the Spearfish formation.  These massive beds are sometimes referred to as the Gypsum Springs formation.

The chemical formula for this mineral is: CaSO4 *2H2O

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Hematite

This ore occurs throughout the Black Hills.  Most of the higher quality deposits are found near Nemo, South Dakota west of Rapid City.  Some other deposits of interest are near Keystone.  It occurs in a wide variety of deposits such as a quartz-hematite out crop which is estimated to be 800 to 1,000 feet thick.  

The chemical formula for this mineral is: Fe2O3

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Lepidolite

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This mineral is found in abundance within most of the granite pegmatites in the Black Hills area.  Some of the more desirable deposits are located near Keystone in the Ingersoll mine in association with cleavelandite and quartz.  Most of the lepidolite recovered at this location is lilac to pale-purple in color and have very large crystals, up to 1/2 inch in size.  This deposit contained large masses of the mineral.  Another deposit in the southern Black Hills contained fine grained crystals of lepidolite in association with quartz-spodumene.  

The chemical formula for this mineral is: KLi2Al(Si4O10)(OH,F)2 

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Limestone

Several limestone formations encircle the Black Hills.  The Pahasapa (also known as the Madison) limestone and the Minnekahta limestones are the more prominent and recognizable formations found in the area.  The Pahasapa outcrop provides recharge to Rapid City’s major drinking water supply and the Minnekahta is heavily mined near Rapid City for its high-calcium limestone.

 This rock consists mainly of the mineral calcite (calcium carbonate) which has a chemical formula of CaCO3.

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Magnetite

Magnetite is found within many of the Black Hills igneous, metamorphic, and sedimentary rocks but only in minor concentrations.

 The chemical formula for this mineral is:  (Fe,Mg)Fe2O4

 

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Muscovite

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Muscovite is widespread throughout the entire Black Hills.  Its larger crystals occur primarily within various granites (mostly pegmatites).  It is also found in some of the metamorphic and sedimentary rocks located throughout the Black Hills.

 The chemical formula for this mineral is:  KAl3Si3O10(OH)2

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Plagioclase Feldspars

(Albite, Andesine, Anorthite, Bytownite, Labradorite, and Oligoclase)

 

Albite  

Albite is widespread throughout the Black Hills.  It is the one of the most common constituents of granites, rhyolites, andesite and schists in the area (Roberts and Rapp, 1965).

 The chemical formula for this mineral is:  mNaAlSi3O8 with nCaAl2Si2O8

 Andesine

Andesine is found in the northern Black Hills as a quartz-monzonite porphyry and other basic rocks in the northern Black Hills (Roberts and Rapp, 1965).

 The chemical formula for this mineral is:  mNaAlSi3O8 with nCaAl2Si2O8

 Anorthite

 Anorthite is widespread throughout the central Black Hills and is found in most igneous rocks. 

 The chemical formula for this mineral is:  mCaAl2Si2O8 with nNaAlSiO8

Bytownite

Bytownite has been noted in the Keystone area of the Black Hills within the Bullion formation (Roberts and Rapp, 1965).

 The chemical formula for this mineral is:  mCaAl2Si2O8 with nNaAlSi3O8

 Labradorite

 Labradorite has been noted to be constituents of amphibolites and hornblendes in the northern Black Hills.

 The chemical formula for this mineral is:  mCaAl2Si2O8 with nNaAlSi3O8

 Oligoclase

This mineral is found in various pegmatites in the Black Hills and has been reported to be a major constituent of the Game Lodge granite in Custer County (Roberts and Rapp, 1965).

 The chemical formula for this mineral is:  mNaAlSi3O8 with nCaAl2Si2O8

 

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Potassium Feldspars

(Anorthoclase, Microcline, Orthoclase)

Anorthoclase

Identified only by the microscope, Anorthoclase is found in some of the soda rich phonolite and tinguaite rocks of the northern Black Hills (Roberts and Rapp, 1965).

The chemical formula for this mineral is:  (Na,K)AlSi3O8

Microcline

Occurring in granites, pegmatites, phonolites, and rhyolites, Microcline is one of the Black Hills most abundant minerals (Roberts and Rapp, 1965).

The chemical formula for this mineral is:  KAlSi3O8

Orthoclase

Orthoclase occurs well crystallized usually within the igneous rocks of the northern Black Hills.  It is found to be the main constituent of syenite, trachyte, rhyolites, phonolites, and tinguaite rocks in Lawrence County (Roberts and Rapp, 1965).

The chemical formula for this mineral is:  KAlSi3O8

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Pyrope

This mineral is one of the six that are part of the garnet group.  Although garnets occur throughout the Black Hills area, only traces of pyrope are generally found within various pegmatites (Roberts and Rapp, 1965).

 The chemical formula for this mineral is:  Mg3Al2(SiO4)3

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Quartz

Quartz is one of the most common minerals in the Black Hills and is found in igneous, metamorphic, and sedimentary rocks.  It forms as regular crystals in granite and is common in most gneiss, schist, and quartzites in the area. 

The chemical formula for this mineral is:  SiO2

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Rare Earth Elements

Rare earth elements are oxides of a series of fifteen metallic elements, from lanthanum (atomic number 57) to lutetium (atomic number 71) and the three other elements:  yttrium, thorium, and scandium (Bates and Jackson, 1984).  Some of these elements occur in vein deposits in the tertiary intrusive and Paleozoic rocks (Roberts and Rapp, 1965).  The veins in which these elements occur are located mostly in the Bear Lodge district of Wyoming just north of Sundance.

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Sand & Gravel

Sand and gravel is mined throughout the Black Hills mainly for road construction purposes.  In 2002, sand and gravel was the major non-metallic mineral commodity produced throughout the state of South Dakota (Holm, Cline, and Nelson, 2003).

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Scheelite

Scheelite is found in contact metamorphic deposits of granitic intrusions in limestone (Roberts and Rapp, 1965).  In the Black Hills, Scheelite can also be found in various quartz veins, pegmatites, and placer deposits.

 The chemical formula for this mineral is:  CaWO4

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Schorl

Schorl is a variety of tourmaline given its name due to its Black color.  Tourmaline is an accessory mineral to most igneous rocks occurring in the Black Hills

 The chemical formula for this mineral is:  Na(Fe,Mn)3Al6B3Si6O27(OH,F)4

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Shale

Several formations containing shale surround the Black Hills.  With deposition in the Paleozoic and Mesozoic, the shales vary in color, thickness, and composition.  Some of the major shales are found in the Opeche shale, Spearfish formation, Sundance formation, and cretaceous Graneros shale.

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Slate

This low-grade metamorphic rock can be found throughout the central Black Hills (Roberts and Rapp, 1965).  Slate is currently used for construction of blackboards and roofing.

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Spessartite

Spessartite is one of the six minerals that are part of the garnet group.  This dark brown trapezohedral garnet is found in several small pegmatites near the town of Custer, South Dakota (Roberts and Rapp, 1965).

 The chemical formula for this mineral is:  Mn3Al2(SiO4)3

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Spodumene

Spodumene is found in several granite pegmatites located in Custer, Lawrence, and Pennington counties of the Black Hills (Roberts and Rapp, 1965).  Spodumene is mined primarily for its lithium content.

 The chemical formula for this mineral is:  LiAlSi2O6

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Talc

Talc is a soft secondary mineral formed by the hydration of magnesium silicate in igneous rocks (Bates and Jackson, 1984).  Large masses of talc can be found in various pegmatites of the northern Black Hills.  Talc can be used as a filter, coating, dusting agent, in ceramics, rubber, plastics, and lubricants (Roberts and Rapp, 1965).

 The chemical formula for this mineral is:  Mg3Si4O10(OH)2

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Wolframite

Wolframite is found in quartz veins, pegmatites, and placer deposits in the Tinton district of the southern Black Hills.  It also occurs as replacement deposits of dolomite sandstones in Lawrence County (Roberts and Rapp, 1965).  Wolframite is the main ore of tungsten.

The chemical formula for this mineral is:  (Fe, Mn)WO4

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Zircon

Zircon is widely distributed throughout the Black Hills as an accessory constituent of many igneous and metamorphic rocks along with placer deposits.  Although most occurrences are microscopic, larger crystals were collected from the Tin Mountain mine west of Custer, South Dakota (Roberts and Rapp, 1965).

 The chemical formula for this mineral is:  ZrSiO4

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