Bustamite is a calcium manganese

inosilicate Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, the crystalline forms of silica (silicon dio ...

(chain silicate) and a member of the

wollastonite Wollastonite is a calcium Silicate minerals, inosilicate mineral (calcium, Casilicon, Sioxygen, O3) that may contain small amounts of iron, magnesium, and manganese substituting for calcium. It is usually white. It forms when impure limestone or D ...

group. Magnesium, zinc and iron are common impurities substituting for manganese. Bustamite is the high-temperature polymorph of CaMnSi₂O₆ and johannsenite is the low temperature polymorph. The inversion takes place at , but may be very slow.Deer, W A, Howie, R A and Zussman, J (1978) Rock-Forming Minerals, 2nd edition, Volume 2A, pages 574-585
Bustamite could be confused with light-colored

rhodonite Rhodonite is a manganese inosilicate, with the formula (Mn, Fe, Mg, Ca)SiO3, and member of the pyroxenoid group of minerals, crystallizing in the triclinic system. It commonly occurs as cleavable to compact masses with a rose-red color (its na ...

or pyroxmangite, but both these minerals are biaxial (+) whereas bustamite is biaxial (−).

Cell parameters

There is considerable variety in the literature about the size and type of the

unit cell In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector In mathematics, a unit vector i ...

, the formula to be used, and the value of Z, the number of formula units per unit cell. Bustamite is a

triclinic class=skin-invert-image, 180px, Triclinic (a ≠ b ≠ c ≠ a and α, β, γ, 90° pairwise different) In crystallography, the triclinic (or anorthic) crystal system is one of the seven crystal systems. A crystal system is described by three b ...

mineral, which could be described by a primitive unit cell, but the larger A-centered cell is often preferred, in order to facilitate comparison with the similar mineral

.Peacor and Prewitt (1963) The American Mineralogist volume 48 pages 588 to 596 The formula for bustamite is but it is sometimes written , and changing the formula in this way will change the value of Z. The structure is chains of SiO₄ tetrahedra with repeat unit of three tetrahedra, unlike the

pyroxenes The pyroxenes (commonly abbreviated Px) are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents ions of calcium (Ca), sodium (Na), iron (Fe( ...

where the repeat unit is two. Ca⁺⁺ and Mn⁺⁺ are positioned between the chains. There are 12 tetrahedra in the A-centered unit cell. The unit cell, the formula and Z cannot be taken separately; they are interlinked and form a consistent set of values. This article adopts the A-centred unit cell (space group A) with a = 7.736 Å, b = 7.157 Å and c = 13.824 Å, the formula and Z = 6. Deer et al. take the formula as so their value of Z is doubled to 12. Mindat apparently gives the lattice parameters for a face-centred cell, although they give the space group as P.

Type locality

The type locality was originally taken as Tetela de Jonotla,

Puebla Puebla, officially the Free and Sovereign State of Puebla, is one of the 31 states that, along with Mexico City, comprise the Federal Entities of Mexico. It is divided into 217 municipalities and its capital is Puebla City. Part of east-centr ...

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

, and the mineral was named for the Mexican mineralogist José María Bustamante y Septiem, professor at the Mexico Mining Seminary. The material from Puebla, however, was later found to be a mixture of johannsenite and

,Dana's New Mineralogy Eighth Edition, Wiley so the type locality is now the Franklin Mine, Franklin,

Sussex County, New Jersey Sussex County () is the northernmost county in the U.S. state of New Jersey. Its county seat is Newton. Both bustamite and johansennite are found at Franklin. Bustamite is moderately common there and occurs in a variety of assemblages, associated with rhodonite and

tephroite Tephroite is the manganese endmember of the olivine group of nesosilicate minerals with the formula Mn2 Si O4. A solid solution series exists between tephroite and its analogues, the group endmembers fayalite and forsterite. Divalent iron or m ...

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

and tephroite or glaucochroite and tephroite.

Vesuvianite Vesuvianite, also known as idocrase, is a green, brown, yellow, or blue silicate mineral. Vesuvianite occurs as tetragonal crystals in skarn deposits and limestones that have been subjected to contact metamorphism. It was first discovered withi ...

, wollastonite,

garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. Garnet minerals, while sharing similar physical and crystallographic properties, exhibit a wide range of chemical compositions, de ...

diopside Diopside is a monoclinic pyroxene mineral with composition . It forms complete solid solution series with hedenbergite () and augite, and partial solid solutions with orthopyroxene and pigeonite. It forms variably colored, but typically dull ...

willemite Willemite is a zinc silicate mineral () and a minor ore of zinc. It is highly fluorescent (green) under shortwave ultraviolet light. It occurs in a variety of colors in daylight, in fibrous masses and apple-green gemmy masses. Troostite is a vari ...

, johannsenite, margarosanite and clinohedrite also may be present.

Environment

Bustamite typically results from

metamorphism Metamorphism is the transformation of existing Rock (geology), rock (the protolith) to rock with a different mineral composition or Texture (geology), texture. Metamorphism takes place at temperatures in excess of , and often also at elevated ...

of manganese-bearing sediments, with attendant

metasomatism Metasomatism (from the Greek μετά ''metá'' "change" and σῶμα ''sôma'' "body") is the chemical alteration of a rock by hydrothermal and other fluids. It is traditionally defined as metamorphism which involves a change in the chemical com ...

. At the (new) type locality, Franklin, the oldest rocks are

Precambrian The Precambrian ( ; or pre-Cambrian, sometimes abbreviated pC, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of t ...

gneisses of mixed sedimentary and volcanic origin. Franklin Marble was deposited within these rocks, along with sediments containing zinc, manganese and iron minerals. These sediments were metamorphosed later in the Precambrian, then the rocks were uplifted from the late Precambrian into the

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

and

quartzite Quartzite is a hard, non- foliated metamorphic rock that was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tecton ...

was deposited on the eroded surface. In Cambrian-

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

time the quartzite was in turn overlain by

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

, and the rocks have been subject to uplift and erosion up to the present time.Drake, A A (1990) The regional geologic setting of the Franklin-Sterling Hill district. Symposium on the character and origin of the Franklin-Sterling Hill orebodies, Proceedings, pp. 14-31, Lehigh University, Bethlehem, Pennsylvania

References

External links

{{Commons category, Bustamite Inosilicates Triclinic minerals Minerals in space group 2