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Quartz

 

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Quartz  (Click PPL image to show labels)

Olivine

 

Quartz from granite. Lack of obvious distinguishing features in PPL can itself be a useful aid to identification. Quartz is often one of the last minerals to crystallise from a melt, so occurs in areas between better formed minerals. Good euhedral crystals are not common. Clear areas in suitable rock types are often quartz, alternative minerals that can be taken for quartz are much more rare. See cordierite, andalusite, topaz.

 

Width of field of view: 10mm.

 

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Olivine XPL view

 

Quartz from granite. Cloudy extinction is very common, and a strong indicator for the mineral. This view also shows sutured joints between the grains, both indicate strain and recrystallization. Twinning not seen in quartz. Low birefringence, max colour is described as pale cream or straw, but yellow often seen if section is slightly thicker than standard.

 

Width of field of view: 10mm.

 

 

   

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Cloudy

Extinction

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Olivine rollover

 

Quartz vein in mica schist

 

Width of field of view: 15mm.

 

 

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Quartz vein in mica schist, recrystallised, and with sutured margins

 

Width of field of view: 15mm.

 

 

 

   

 

   

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Olivine rollover

 

Quartz granophyric intergrowth texture. simultaneous crystallisation of quartz and alkali feldspar, often, as in this slide, nucleated on plagioclase. This texture is seen in shallow intrusions, veins and pegmatites

 

Width of field of view: 10mm.

 

 

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Quartz in granophyre. Although the individual parts of the texture are small, the extent of the whole crystal can be seen by the area that extinguishes at the same angle. The cause of granophyric texture as been the subject of debate, but is possibly caused by rapid loss of volatile compounds and decompression in an undercooled melt.

 

Width of field of view: 10mm.

 

 

 

   

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Extinction

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Olivine rollover

 

Quartz as agate from fossilised dinosaur bone. Concentric rings a occasional layering visible through seconday staining.

 

Width of field of view: 10mm.

 

 

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Quartz as agate. repeated layers of very fine grained radial needles.

 

Width of field of view: 10mm.

 

 

 

   

 

   

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Olivine rollover

 

Quartz in pegmatitic granite, Ben Nevis. Subhedral embayed phenocrysts of quartz in a fine grained matrix of quartz and feldspar.

 

Width of field of view: 10mm.

 

 

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Quartz Embayed euhedral quartz phenocrysts in a fine grained quartz/feldspar matrix. Porphyritic texture. Unusual texture for a granite.

 

Width of field of view: 10mm.

 

 

 

   

 

   

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Olivine rollover

 

Quartz Rounded quartz grains in Spilsby Sandstone. Calcite cement matrix. Glauconite indicates this sandstone is of marine origin..

 

Width of field of view: 10mm.

 

 

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Quartz in sandstone. Most grains in this view are quartz, some feldspar is visible showing twinning.

 

Width of field of view: 10mm.

 

 

 

   

 

   

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