Editing Ulexite (section)

== Optical properties ==
[[File:Ulexite-39574.jpg|thumb|A fragment of ulexite displaying characteristic optical property]]

In 1956, John Marmon observed that fibrous aggregates of ulexite project an image of an object on the opposite surface of the mineral. This optical property is common for synthetic fibers, but not in minerals, giving ulexite the nickname "TV rock".  According to Baur et al. (1957),<ref name="BaurLarsenSand1957">{{cite journal | url=http://www.minsocam.org/msa/collectors_corner/arc/ulexitefiberoptic.htm | title=Image projection by fibrous minerals | last1 =Baur  | first1 =G.S. | last2 =Larsen | first2 =W.N. | last3 =Sand | first3 =L.B. | journal=American Mineralogist | year=1957 | volume=42 | pages=697–699}}</ref> this optical property is due to the reflections along twinned fibers, the most prominent twinning plane being on (010). The light is internally reflected over and over within each of the fibers that are surrounded by a medium of a lower refractive index (Garlick, 1991).<ref name = Garlick>{{cite journal |last1=Garlick |first1=G. Donald |last2=Kamb |first2=W. Barclay |title=The strange optical properties of Ulexite |journal=Journal of Geological Education |date=1991 |volume=39 |issue=5 |pages=398–402|doi=10.5408/0022-1368-39.5.398 |bibcode=1991JGeoE..39..398G |doi-access=free }}</ref> This optical effect is also the result of the large spaces formed by the sodium octahedral chains in the mineral structure. Synthetic fibers used for fiber optics transmit images along a bundle of threadlike crystals the same way naturally occurring ulexite reproduces images due to the existence of different indices of refractions between fibers. Additionally, if the object is colored, all of the colors are reproduced by ulexite. Parallel surfaces of ulexite cut perpendicular to the fibers produce the best image, as distortion in the size of the projected image will occur if the surface is not parallel to the mineral. Curiously, ''in situ'' samples of ulexite are capable of producing a decent, rough image. Satin spar gypsum also exhibits this optical effect; however, the fibers are too coarse to transmit a decent image. The thickness of the fibers is proportional to the sharpness of the projected image.<ref name="BaurLarsenSand1957"/>

Ulexite also displays concentric circles of light if held up to a bright light source, a strange optical property first observed by G. Donald Garlick (1991).<ref name="Garlick" /> This effect can also be produced by shining a laser pointer at a slightly oblique angle through a piece of ulexite. This optical behavior is a consequence of the different refractive indices of ulexite in different directions of polarization. Microscopic analysis of ulexite also yields cones of light that clearly emerge from each grain that is thicker than 0.1&nbsp;mm under the Bertrand lens.

Ulexite is colorless and [[Pleochroism | nonpleochroic]] in thin sections with low relief. Being [[Triclinic crystal system | triclinic]], ulexite is [[Optic axis of a crystal | optically biaxial]]. Interference figures yield addition on the concave side of the [[Conoscopic interference pattern | isogyres]], causing ulexite to be biaxial positive. Ulexite has a high [[Conoscopic interference pattern | 2V ]] that ranges between 73° – 78° and a maximum [[birefringence]] of up to 0.0300 (Anthony et al., 2005).<ref name="Anthony" /> According to Weichel-Moore and Potter (1963),<ref name = Weichel-Moore>{{cite journal |last1=Weichel-Moore |first1=E.J. |last2=Potter |first2=R.J. |title=Fibre optical properties of ulexite |journal=Nature |date=1963 |volume=200 |issue=4912 |pages=1163–1165|doi=10.1038/2001163b0 |bibcode=1963Natur.200.1163W |s2cid=4192912 }}</ref> the orientation of the fibers around the [[Crystal structure | c-axis]] is completely random based on the variations in extinctions viewed under cross polarization. Ulexite displays polysynthetic twinning parallel to the elongation, along {010} and {100} (Murdoch, 1940).<ref name="Murdoch" /> In thin sections cut parallel to the fibers, ulexite grains display both length-fast and length-slow orientations in equal quantities because the intermediate axis (y) of the indicatrix is roughly parallel to the elongation of the fibers along the crystallographic c-axis (Weichel-Moore and Potter, 1963).<ref name = "Weichel-Moore" />