Topaz - Al2SiO4(F,OH)2

The name topaz is usually derived (via Old French: topace and Latin: topazus) from the Greek (topazios), the ancient name of Zeberget Island (Topasos) in the Red Sea from which a yellow stone (now believed to be olivine) was mined in ancient times. Pliny said that Topazos is a legendary island in the Red Sea and the mineral "topaz" was first mined there. Alternatively, the word topaz may be related to the Sanskrit word "tapas" meaning "heat" or "fire".

The structure of Topaz cosists of tetrahedral SiO4 groups together with linked octahedral AlO6 groups: 4 of the 6 anions around each Al are oxygens belonging to the SiO4 groups, the other being or F or hydroxyl ions.
The composition of topaz is fairly constant, the only major variation being in the ratio of F to hydroxyl ions

Topaz occurs in igneous rocks (granites, rhyolites). It is also a mineral which occurs in tin-bearing pegmatites and in tin veins generally, formed through the agency of fluorine bearing pneumatolytic fluid vapors given off during the last stages of the solidification of igneous rocks. In these environments it is found in cavities in rhyolite lavas and granite associated with related minerals including fluorite, cassiterite, and tourmaline, apatite, etc. Topaz is also found associated in pegmatites with quartz, mica, feldspar. Because it is highly durable and hard, it is found at times in alluvial deposits as water rolled pebbles in stream sands.

Optical Properties:
Form: Short columns, acicular parallel to the c-axis or brush-like (pycnite); typical as single granules.
Relief: High.
Cleavage: Very good on (001).
Color: Colourless.
Interference colors: Low birefringence (grey-white to straw-yellow interference colours of the 1st order).
Special characteristics: Tends to be rich in fluid inclusions.


Bibliography



• Deer, W.A., Howie, R.A., Zussman, J. (1998) Rock-forming Minerals.
• Nesse, William D., 1986, Introduction to Optical Mineralogy: New York, Oxford University Press




Photo
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Topaz (colorless, High relief) and quartz in a greisen. Zinnwald, Saxony, Germany. PPL image, 1x (Field of view = 9mm)
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Topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 1x (Field of view = 9mm)
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Topaz (colorless, High relief) and quartz in a greisen. Zinnwald, Saxony, Germany. PPL image, 2x (Field of view = 7mm)
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Topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 2x (Field of view = 7mm)
greisen(23).jpg

Topaz (colorless, High relief) and quartz in a greisen. Zinnwald, Saxony, Germany. PPL image, 2x (Field of view = 7mm)
greisen(24).jpg

Topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 2x (Field of view = 7mm)
greisen(25).jpg

Topaz (colorless, High relief) and quartz in a greisen. Zinnwald, Saxony, Germany. PPL image, 2x (Field of view = 7mm)
greisen(26).jpg

Topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 2x (Field of view = 7mm)
greisen(41).jpg

Topaz (colorless, High relief) and quartz in a greisen. Zinnwald, Saxony, Germany. PPL image, 2x (Field of view = 7mm)
greisen(42).jpg

Topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 2x (Field of view = 7mm)
greisen(26).jpg

Topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 2x (Field of view = 7mm)
greisen(44).jpg

Topaz (colorless, High relief) and quartz in a greisen. Zinnwald, Saxony, Germany. PPL image, 2x (Field of view = 7mm)
greisen(45).jpg

Topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 2x (Field of view = 7mm)
greisen(52).jpg

Topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 2x (Field of view = 7mm)
greisen(54).jpg

Topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 2x (Field of view = 7mm)
greisen(64).jpg

Topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 10x (Field of view = 2mm)
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Topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 10x (Field of view = 2mm)
greisen(75).jpg

Topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 10x (Field of view = 2mm)
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Topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 10x (Field of view = 2mm)
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Topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 10x (Field of view = 2mm)
greisen(82).jpg

Topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 10x (Field of view = 2mm)
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Topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 1x (Field of view = 9mm)
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Zinnwaldite (micaceous habit), topaz (high relief, colorless) and quartz in a greisen. Zinnwald, Saxony, Germany. PPL image, 1x (Field of view = 9mm)
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Zinnwaldite (high interference colors), topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 1x (Field of view = 9mm)
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Zinnwaldite (micaceous habit), topaz (high relief, colorless) and quartz in a greisen. Zinnwald, Saxony, Germany. PPL image, 1x (Field of view = 9mm)
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Zinnwaldite (high interference colors), topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 1x (Field of view = 9mm)
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Topaz (high relief, colorless) and quartz in a greisen. Zinnwald, Saxony, Germany. PPL image, 1x (Field of view = 9mm)
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Zinnwaldite (micaceous habit), topaz (high relief, colorless) and quartz in a greisen. Zinnwald, Saxony, Germany. PPL image, 1x (Field of view = 9mm)
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Zinnwaldite (high interference colors), topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 2x (Field of view = 7mm)
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Zinnwaldite (high interference colors), topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 2x (Field of view = 7mm)
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Zinnwaldite (high interference colors), topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 2x (Field of view = 7mm)
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Zinnwaldite (micaceous habit), topaz (high relief, colorless) and quartz in a greisen. Zinnwald, Saxony, Germany. PPL image, 1x (Field of view = 9mm)
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Zinnwaldite (high interference colors), topaz (I order gray) and quartz in a greisen. Zinnwald, Saxony, Germany. XPL image, 2x (Field of view = 7mm)
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Topaz (I order gray), Zinnwaldite (high interference colors). Zinnwald, Saxony, Germany, XPL image 10x (Field of view = 2mm)
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Topaz (I order gray), Zinnwaldite (high interference colors). Zinnwald, Saxony, Germany, XPL image 10x (Field of view = 2mm)
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Topaz (I order gray), Zinnwaldite (high interference colors). Zinnwald, Saxony, Germany, XPL image 10x (Field of view = 2mm)