THE MINERAL BYTOWNITE

  • Chemistry: Ca(70-90%) Na(30-10%) (Al, Si)AlSi2 O8, Calcium sodium aluminum silicate.
  • Class: Silicates
  • Subclass: Tectosilicates
  • Group: Feldspars
  • Uses: only as a mineral specimen.
  • Specimens

Bytownite is a rather rare member plagioclase series. The plagioclase series comprises minerals that range in chemical composition from pure NaAlSi3 O8, Albite to pure CaAl2 Si2 O8 , anorthite. Bytownite by definition must contain 30-10% sodium to 70-90% calcium in the sodium/calcium position in the crystal structure. The various plagioclase feldspars are identified from each other by gradations in index of refraction and density in the absence of chemical analysis and/or optical measurements.

All plagioclase feldspars show a type of twinning that is named after albite. Albite Law twinning produces stacks of twin layers that are typically only fractions of millimeters to several millimeters thick. These twinned layers can be seen as striation like grooves on the surface of the crystal and unlike true striations these also appear on the cleavage surfaces. The Carlsbad Law twin produces what appears to be two intergrown crystals growing in opposite directions. Two different twin laws, the Manebach and Baveno laws, produce crystals with one prominant mirror plane and penetrant angles or notches into the crystal. Although twinned crystals are common, single crystals showing a perfect twin are rare and are often collected by twin fanciers.

PHYSICAL CHARACTERISTICS:

  • Color is usually white, gray or colorless but can be pale shades of other colors.
  • Luster is vitreous to dull if weathered..
  • Transparency crystals are translucent to opaque and only sometimes transparent.
  • Crystal System is triclinic; bar 1
  • Crystal Habits include blocky, or tabular crystals. Rarely are free crystals seen but they have a nearly rectangular or square cross-section with slanted dome and pinacoid terminations. Twinning is almost universal in all plagioclases. Crystals can be twinned according to the Albite, Carlsbad, Manebach and Baveno laws. Bytownite is usually found as grains in gabbros and in compact masses.
  • Cleavage is perfect in one and good in another direction forming nearly right angled prisms.
  • Fracture is conchoidal.
  • Hardness is 6 - 6.5.
  • Specific Gravity is approximately 2.74-2.76 (average)
  • Streak is white.
  • Associated Minerals are biotite, hornblende and pyroxenes.
  • Other Characteristics: index of refraction is 1.565 to 1.585. Lamellar twinning may cause a grooved effect on cystal and cleavage surfaces that appear as striations.
  • Notable Occurrences include Ottawa (formally Bytown), Canada; Scotland and South Africa.
  • Best Field Indicators are occurence, twinning striations, density and index of refraction.
BYTOWNITE specimens:
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BYTOWNITE specimen byt-1
$ 80.00
Dims: 2.5 x 1.3 x 0.8" (6.4 x 3.3 x 2.0 cm)
Wt: 1.82 oz. (51,6 g)
Chihuahua, Mexico
This large thumbnail specimen consists of a partial crystal of Bytownite, a variety of Plagioclase feldspar. It appears to be considerably damaged, possessing several conchoidal fracture surfaces, but most of these appear to be slightly worn, so I cannot tell whether they occured prior to or after mining. The piece shows visible but indefinite triclinic prismatic form- a few definite, striated faces are quite obvious, but an actual form cannot be determined. It has a pale, dull-yellow coloration and a luster that ranges from dull waxy to pearly, and is transparent and dimly to moderately clear. There is no host or base material present.
no photo
byt-1 ($ 80.00)
Chihuahua, Mexico
BYTOWNITE specimen byt-2
$ 46.00
Dims: 1.7 x 1.5 x 0.6" (4.3 x 3.8 x 1.5 cm)
Wt: 1.04 oz. (29.6 g)
Chihuahua, Mexico
This specimen appears to consist of a single fragment of a larger Bytownite crystal. All faces and edges are curved and conchoidal, so there is no evidence of any crystal shape. The material has a pale yellow color and a pearly luster, and is transparent and seemingly very clear- I see only two obvious internal fractures, and no inclusions. There is no host rock present. This piece likely is excellent faceting material.
no photo
byt-2 ($ 46.00)
Chihuahua, Mexico
BYTOWNITE specimen byt-3
$ 48.00
Dims: 1.9 x 0.8 x 0.6" (4.8 x 2.0 x 1.5 cm)
Wt: 1.08 oz. (30.6 g)
Chihuahua, Mexico
This Bytownite piece shows a small amount of fresh damage in the form of conchoidal surfaces, but is generally in good condition. Its triclinic prismatic form is warped and incomplete, but it still shows definite evidence of its crystalline shape: a few straight edges and flat faces that possess a rather dull pearly-to-waxy luster likely caused by weathering. The piece has a pale yellow coloration and is transparent and moderately clear, containing several internal fractures but few inclusions, if any. When viewed at certain angles, it reveals a rather bright glow that is reminiscent of moonstone- the enclosed documentation refers to it as "sunstone", though this is technically incorrect.
no photo
byt-3 ($ 48.00)
Chihuahua, Mexico
BYTOWNITE specimen byt-4
$ 36.00
Dims: 1.3 x 1.1 x 0.7" (3.3 x 2.8 x 1.8 cm)
Wt: 23.2 g
Chihuahua, Mexico
There is one partial face on this small Bytownite specimen that may be part of a natural crystal face. It is flat, relatively clean, and has a dull waxy luster. All other surfaces are curved and show conchoidal patterns. They also have a much brighter, pearly-to-vitreous luster. These conchoidal faces give one a clear view into the material, which is impressively clear- only one or two internal fractures are visible, and there are no inclusions. It has the standard pale yellow coloration of Bytownite from this locality. There is no base or host rock present. I think that such a piece would be ideal for faceting.
no photo
byt-4 ($ 36.00)
Chihuahua, Mexico
BYTOWNITE specimen byt-5
$ 44.00
Dims: 2.1 x 0.8 x 0.8" (5.3 x 2.0 x 2.0 cm)
Wt: 1.02 oz. (29.0 g)
Chihuahua, Mexico
This specimen consists of a heavily worn and rounded Bytownite piece. It does still have some crystalline tendencies, however- some heavy, parallel striations traverse one uneven face. Other than the natural wear, it appears to be undamaged. All of the other surfaces, however, completely lack any visible crystal form, and all surfaces tend to have a dull pearly to a matte luster. The Bytownite has the pale yellow color that is standard for this locality, and is likely transparent and at least moderately clear- however, given the roughness of the surface of the specimen, that is nearly impossible to detect.
no photo
byt-5 ($ 44.00)
Chihuahua, Mexico
BYTOWNITE specimen byt-6
$ 31.00
Dims: 1.9 x 1.2 x 0.6" (4.8 x 3.0 x 1.5 cm)
Wt: 19.7 g
Chihuahua, Mexico
A single, heavily weathered piece of Bytownite makes up this thumbnail specimen. Though it does not appear to have any fresh damage, it is so heavily worn that it has no definite crystal form. However, some crystalline tendencies are evident, as are a few nearly flat faces that may have been crsytal faces. All surfaces are rough and pitted, giving the piece a mostly dull, waxy luster. It has a pale yellow coloration and appears to be transparent and at least moderately clear. There is no host rock present.
no photo
byt-6 ($ 31.00)
Chihuahua, Mexico
BYTOWNITE specimen byt-7
$ 31.00
Dims: 1.2 x 0.8 x 0.5" (3.0 x 2.0 x 1.3 cm)
Wt: 19.4 g
Chihuahua, Mexico
This specimen consists of a small, misshapen piece of Bytownite. Apart from a few small chips along one edge, the piece shows no fresh damage. Nor does it show any definite crystal form, though the remains of one or two crystal faces may be present- most edges and faces are rough and uneven, and have undergone some wear. There is one flat face, however, that was most likely caused by cleavage along its one perfect cleavage plane- the face is quite clean, and there is evidence that sheets of the material could be cleaved rather easily off of this face. The Bytownite has a dull, pale yellow color and a dull pearly-to-waxy luster, and appears to be transparent and quite clear, though a few internal fractures are visible.
no photo
byt-7 ($ 31.00)
Chihuahua, Mexico
BYTOWNITE specimen byt-8
$ 29.00
Dims: 1.6 x 1.0 x 0.7" (4.1 x 2.5 x 1.8 cm)
Wt: 18.5 g
Chihuahua, Mexico
A rather thin, shapeless Bytownite chunk makes up this thumbnail specimen. The piece is somewhat weathered but shows no fresh damage. Nor does it show any appreciable crystal form, as all edges and faces are curved or uneven. It has a dull, pale yellow coloration and a dull matte-to-vitreous luster, and appears to be transparent and quite clear, though its surface patina makes this difficult to confirm. What I first thought was some type of a host rock is apparently several encrustations of organic matter (probably a lichen or moss) that have partly covered the stone.
no photo
byt-8 ($ 29.00)
Chihuahua, Mexico
BYTOWNITE specimen byt-9
$ 26.00
Dims: 1.6 x 1.0 x 0.7" (4.1 x 2.5 x 1.8 cm)
Wt: 18.4 g
Chihuahua, Mexico
This thumbnail specimen consists of a rather shapeless chunk of crystalline Bytownite. It shows only one small spot of recent damage, so I think that the breakage that caused its uneven shape occurred before it was mined. All faces edges are generally curved or uneven, and the faces possess a dull, nearly matte luster. The material has a dull, pale golden coloration and is likely transparent and clear, though the dull patina on its surface makes this difficult to see. There are a few crusts of what I believe are a moss or lichen coating parts of the piece, but there is no host rock present.
no photo
byt-9 ($ 26.00)
Chihuahua, Mexico
BYTOWNITE specimen byt-10
$ 25.00
Dims: 1.6 x 0.5 x 0.4" (4.1 x 1.3 x 1.0 cm)
Wt: 10.1 g
Chihuahua, Mexico
A small, misshapen piece of crystalline Bytownite comprises this specimen. It is in fair condition, showing heavy breakage and cleavage, and shows only vestiges of a crystalline form, as part of only one natural face is intact. The material has a dull, pale yellow coloration and a dull luster (though the freshly broken faces possess a bright, almost vitreous luster) and is transparent and very clear. There is no host rock present.
no photo
byt-10 ($ 25.00)
Chihuahua, Mexico
 

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