Strontianite
Strontianite | ||
---|---|---|
2V angle Measured: 7°, Calculated: 12° to 8° | | |
Ultraviolet fluorescence | Almost always fluorescent | |
Solubility | Soluble in dilute HCl | |
Alters to | Celestine SrSO4 | |
References | [2][3][4][5] |
Strontianite (SrCO3) is an important raw material for the extraction of strontium. It is a rare carbonate mineral and one of only a few strontium minerals. It is a member of the aragonite group.
Aragonite group members:[2] aragonite (CaCO3), witherite (BaCO3), strontianite (SrCO3), cerussite (PbCO3)
The ideal formula of strontianite is SrCO3, with molar mass 147.63 g,[4] but calcium (Ca) can substitute for up to 27% of the strontium (Sr) cations, and barium (Ba) up to 3.3%.[2]
The mineral was named in 1791 for the locality, Strontian, Argyllshire, Scotland, where the element strontium had been discovered the previous year.[2] Although good mineral specimens of strontianite are rare, strontium is a fairly common element, with abundance in the Earth's crust of 370 parts per million by weight, 87 parts per million by moles, much more common than copper with only 60 parts per million by weight, 19 by moles.[6] Strontium is never found free in nature. The principal strontium ores are celestine SrSO4 and strontianite SrCO3. The main commercial process for strontium metal production is reduction of strontium oxide with aluminium.[6]
Unit cell
Strontianite is an orthorhombic mineral, belonging to the most symmetrical class in this system, 2/m 2/m 2/m, whose general form is a rhombic dipyramid. The space group is Pmcn. There are four formula units per unit cell (Z = 4) and the unit cell parameters are a = 5.1 Å, b = 8.4 Å, c = 6.0 Å.
Structure
Strontianite is
The CO3 group is slightly non-planar; the carbon atom lies 0.007 Å out of the plane of the oxygen atoms. The groups are tilted such that the angle between a plane drawn through the oxygen atoms and a plane parallel to the a-b unit cell plane is 2°40’.[8]
Crystal form
Strontianite occurs in several different habits. Crystals are short prismatic parallel to the c axis and often acicular.[2][3][5] Calcium-rich varieties often show steep pyramidal forms.[2] Crystals may be pseudo hexagonal[2][3][5] due to equal development of different forms.[3] Prism faces are striated horizontally.[2][3] The mineral also occurs as columnar to fibrous, granular or rounded masses.[2][3][5]
Optical properties
Strontianite is colourless, white, gray, light yellow, green or brown, colourless in transmitted light. It may be longitudinally zoned. It is transparent to translucent, with a vitreous (glassy) lustre, resinous on broken surfaces, and a white streak.
It is a biaxial(−) mineral. The direction perpendicular to the plane containing the two optic axes is called the optical direction Y. In strontianite Y is parallel to the b crystal axis. The optical direction Z lies in the plane containing the two optic axes and bisects the acute angle between them. In strontianite Z is parallel to the a crystal axis. The third direction X, perpendicular both to Y and to Z, is parallel to the c crystal axis.[2][5] The refractive indices are close to nα = 1.52, nβ = 1.66, nγ = 1.67, with different sources quoting slightly different values:
- nα = 1.520, nβ = 1.667, nγ = 1.669[2]
- nα = 1.516 – 1.520, nβ = 1.664 – 1.667, nγ = 1.666 – 1.668[3][4]
- nα = 1.517, nβ = 1.663, nγ = 1.667 (synthetic material)[9]
The maximum birefringence δ is 0.15[3] and the measured value of 2V is 7°, calculated 12° to 8°.[3][4]
If the colour of the incident light is changed, then the refractive indices are modified, and the value of 2V changes. This is known as dispersion of the optic axes. For strontianite the effect is weak, with 2V larger for violet light than for red light r < v.[5]
Luminescence
Strontianite is almost always
Physical properties
Cleavage is nearly perfect parallel to one set of prism faces, {110}, and poor on {021}. Traces of cleavage have been observed on {010}.[3][5]
Twinning is very common, with twin plane {110}. The twins are usually contact twins; in a contact twin the two individuals appear to be reflections of each other in the twin plane. Penetration twins of strontainite are rarer; penetration twins are made up of interpenetrating individuals that are related to each other by rotation about a twin axis. Repeated twins are made up of three or more individuals twinned according to the same law. If all the twin planes are parallel then the twin is polysynthetic, otherwise it is cyclic.[7] In strontianite repeated twinning forms cyclic twins with three or four individuals, or polysynthetic twins.[2][3][5]
The mineral is brittle, and breaks with a subconchoidal to uneven
Environment and associations
Strontianite is an uncommon low-temperature
Occurrences
Type locality
The
Other UK localities include Brownley Hill Mine (Bloomsberry Horse Level), Nenthead,
Canada
The Francon quarry,
Strontianite is very common at the Francon Quarry, in a great variety of habits. It is a late stage mineral, sometimes found as multiple generations. It is found as translucent to opaque, white to pale yellow or beige generally smooth surfaced spheroids, hemispheres and compact spherical and botryoidal aggregates to 10 cm in diameter, and as spheres consisting of numerous radiating acicular crystals, up to 1 cm across. Also as tufts, parallel bundles, and sheaf-like clusters of fibrous to acicular crystals, and as white, finely granular porcelaneous and waxy globular aggregates. Transparent, pale pink, columnar to tabular sixling twins up to 1 cm in diameter have been found, and aggregates of stacked stellate sixling twins consisting of transparent, pale yellow tabular crystals.[10]
Another Canadian occurrence is at Nepean, Ontario, in vein deposits in limestone.[2]
Germany
Commercially important deposits occur in
India
In
Mexico
It occurs in the Sierra Mojada District, with celestine in a lead-silver deposit.[2]
Russia
It occurs in the Kirovskii
It also occurs at
United States
In the
At the Minerva Number 1 Mine (Ozark-Mahoning Number 1 Mine) Ozark-Mahoning Group,
In the Silurian Lockport Group, Central and Western New York strontianite is observed in cavities in eastern Lockport, where it occurs as small white radiating sprays of acicular crystals.[16]
In
-
Strontianite from Strontian, Scotland
-
Dresserite and Strontianite from the Francon quarry, Canada
-
Strontianite from the Dreislar Mine, North Rhine-Westphalia, Germany
-
Strontianite from Texas, US
-
Strontianite from Illinois, US
-
Strontianite from California
See also
References
- S2CID 235729616.
- ^ a b c d e f g h i j k l m n o p q r s t u v w x y Gaines et al (1997) Dana’s New Mineralogy Eighth Edition. Wiley
- ^ a b c d e f g h i j k l m n o p Strontianite on Mindat.org retrieved 23/08/11
- ^ a b c d e Barthelmy, Dave. "Strontianite Mineral Data". Retrieved 23 August 2011.
- ^ a b c d e f g h i j k "Strontianite in the Handbook of Mineralogy" (PDF). Retrieved 24 August 2011.
- ^ a b "Strontium". Retrieved 24 August 2011.
- ^ a b c Klein and Hurlbut (1993) Manual of Mineralogy 21st Edition. Wiley
- ^ De Villiers, Johan P R (1971) Crystal Structures of Aragonite, Strontianite and Witherite. The American Mineralogist 56:758
- ^ a b c d Speer, J A and Hensley-Dunn, M L (1976) Strontianite composition and physical properties. American Mineralogist 61:1001–1004
- ^ a b The Mineralogical Record (2006) 37-1:44
- ^ The Mineralogical Record (2010) 41-1:62 supplement
- ^ The Mineralogical Record (2004) 35-4:355
- ^ The Mineralogical Record (2004) 35-2:176
- ^ The Mineralogical Record 35-4:347 (2004)
- ^ Rocks & Minerals (2010) 85-3:212
- ^ Rocks & Minerals (2009) 84-4:332
External links
Media related to Strontianite at Wikimedia Commons