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Bytownite

Mineral: intermediate member of a solid solution series (70 to 90% anorthite and albite)

Field	Value
boxbgcolor	#bd8b59
boxtextcolor	#fff
name	Bytownite
category	Tectosilicate minerals
group	Feldspar group
series	Plagioclase feldspar series
image	Bytownite-mrz296a.jpg
imagesize	170px
caption	A somewhat rounded, alluvial crystal of bytownite from the Dorado Mine, Casas Grandes, Chihuahua, Mexico (size 3.7 × 2 × 1.3 cm)
formula	(Ca,Na)[Al(Al,Si)Si2O8]
strunz	9.FA.35
dana	76.01.03.05
system	Triclinic
class	Pinacoidal ()
(same H-M symbol)
unit cell	a = 8.178 Å, b = 12.870 Å,
c = 14.187 Å; α = 93:5°,
β = 115:9°, γ = 90:63°; Z = 8
color	Colorless, white, gray
habit	Rarely as crystals flattened on [010], commonly as cleavable masses or anhedral grains in massive aggregates
twinning	Common Albite, Carlsbad, and Pericline twinning
cleavage	Perfect on [001], good on [010], imperfect on [110]
fracture	Uneven to conchoidal
tenacity	Brittle
mohs	6 – 6.5
luster	Vitreous, pearly on cleavages
streak	White
diaphaneity	Transparent to translucent
gravity	2.72 – 2.74
opticalprop	Biaxial (+/−)
refractive	nα = 1.563 – 1.572 nβ = 1.568 – 1.578 nγ = 1.573 – 1.583
birefringence	δ = 0.010 – 0.011
2V	Measured: 86°, Calculated: 80° to 88°
dispersion	r v strong
references

(same H-M symbol) c = 14.187 Å; α = 93:5°, β = 115:9°, γ = 90:63°; Z = 8 | length fast/slow = Bytownite is a calcium rich member of the plagioclase solid solution series of feldspar minerals with composition between anorthite and labradorite. It is usually defined as having between 70 and 90%An (formula: ). Like others of the series, bytownite forms grey to white triclinic crystals commonly exhibiting the typical plagioclase twinning and associated fine striations.

The specific gravity of bytownite varies between 2.74 and 2.75. The refractive indices ranges are nα=1.563 – 1.572, nβ=1.568 – 1.578, and nγ=1.573 – 1.583. Precise determination of these two properties with chemical, X-ray diffraction, or petrographic analysis are required for identification.

Occurrence

Bytownite is a rock forming mineral occurring in mafic igneous rocks such as gabbros and anorthosites. It also occurs as phenocrysts in mafic volcanic rocks. It is rare in metamorphic rocks. It is typically associated with pyroxenes and olivine.

The mineral was first described in 1836 and named for an occurrence at Bytown (now Ottawa), Canada. Other noted occurrences in Canada include the Shawmere anorthosite in Foleyet Township, Ontario, and on Yamaska Mountain, near Abbotsford, Quebec. It occurs on Rùm island, Scotland and Eycott Hill, near Keswick, Cumberland, England. It is reported from Naaraodal, Norway and in the Bushveld complex of South Africa. It is also found in Isa Valley, Western Australia.

In the US it is found in the Stillwater igneous complex of Montana; from near Lakeview, Lake County, Oregon. It occurs in the Lucky Cuss mine, Tombstone, Arizona; and from the Grants district, McKinley County, New Mexico. In the eastern US it occurs at Cornwall, Lebanon County, Pennsylvania and Phoenixville, Chester County, Pennsylvania.

References

Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., Wiley,

References

[http://www.mindat.org/min-815.html Mindat with locations]
[http://rruff.geo.arizona.edu/doclib/hom/bytownite.pdf Handbook of Mineralogy]
[http://webmineral.com/data/Bytownite.shtml Webmineral data]
[[Thomas Thomson (chemist)

Info: Wikipedia Source

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calcium-minerals sodium-minerals plagioclase-feldspar-series triclinic-minerals gemstones minerals-in-space-group-2

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