Quartzine

A variety of Chalcedony

Quartzine is a fibrous variety of chalcedony. It is also called "length-slow chalcedony" and is usually intergrown with another, more common type of fibrous chalcedony, "length-fast chalcedony", that comprises most of the different varieties of chalcedony. Length-fast chalcedony is more common than quartzine.

Quartzine "fibers" are made of tiny quartz crystals that are stacked along the c-axis (the long axis of the crystals).

It is not possible to identify quartzine with the naked eye, one needs a polarizing microscope to do that (which is also the reason for the odd names "length-slow" and "length-fast chalcedony" that refer to a special optical property of the chalcedony fibers). However, the peculiar patterns seen in some chalcedony specimen, most notably so-called "feather agates", are caused by the intergrowth of quartzine with "ordinary" length-fast chalcedony (see photo).

Quartzine and length-fast chalcedony give similar extinction patterns in thin sections, in both cases spherulites show a cross-shaped pattern. Although length-fast chalcedony generally looks more fibrous and quartzine more patchy, the safe way to distinguish them is by using a λ-compensator.

The photo to the left shows a small spherulite of length-fast chalcedony that is surrounded by a ring of quartzine, which in turn is embedded in length-fast chalcedony. In spherulitic growth, quartzine shows the yellow color in the upper left and lower right quadrant, rotated by 90 degrees with respect to length-fast chalcedony.

Top: crossed polarizers
Bottom: crossed polarizers with λ-compensator.
Field of view 980µm.