Editing Opal (section)

== Varieties of common opal ==
{{Redirect|Girasol|the American sunflower|Jerusalem artichoke}}
[[File:10 7cts Brazilian Crystal Opal.jpg|thumb|alt=A small, white, trapezoid opal held in someone's hand. Its fire is relatively bright, display a number of finely-grained colours throughout.|Brazilian Precious Opal with patches of brilliant color throughout. The brightness of the fire in opal ranges on a scale of 1 to 5 (with 5 being the brightest)<ref>{{cite book|last=Downing|first=Paul B.|title=Opal Identification and Value|date=1992|pages=55–61}}</ref>]]

"Girasol opal" is a term sometimes mistakenly and improperly used to refer to fire opals, as well as a type of transparent to semitransparent type milky quartz from Madagascar which displays an asterism, or star effect when cut properly. However, the true girasol opal<ref name="LetsTalk"/> is a type of [[hyalite]] opal that exhibits a bluish glow or sheen that follows the light source around. It is not a play of color as seen in precious opal, but rather an effect from microscopic inclusions. It is also sometimes referred to as water opal, too, when it is from Mexico. The two most notable locations of this type of opal are [[Oregon]] and Mexico.<ref>{{Cite web |last=Page |first=Geology |date=2016-06-21 |title=Types of Opal |url=https://www.geologypage.com/2016/06/types-of-opal.html |access-date=2022-12-29 |website=Geology Page |language=en-US}}</ref>

A Peruvian opal (also called blue opal) is a semi-opaque to opaque blue-green stone found in Peru, which is often cut to include the matrix in the more opaque stones. It does not display a play of color. Blue opal also comes from [[Oregon]] and Idaho in the [[Owyhee River|Owyhee]] region, as well as from [[Nevada]] around the [[Virgin Valley]].<ref>{{Cite web|title=Opal – Nevada Mining Association|url=https://www.nevadamining.org/nvma_minerals/opal/|access-date=2020-06-18|website=www.nevadamining.org|date=19 December 2017 }}</ref>

Opal is also formed by [[diatom]]s. Diatoms are a form of algae that, when they die, often form layers at the bottoms of lakes, bays, or oceans. Their cell walls are made up of hydrated silicon dioxide which gives them [[structural coloration]] and therefore the appearance of tiny opals when viewed under a microscope. These cell walls or "tests" form the “grains” for the [[diatomaceous earth]]. This sedimentary rock is white, opaque, and chalky in texture.<ref>{{Cite web|url=http://www.minerals.net/mineral-variety/mineral/diatomite.aspx|title=diatomite – The Mineral and Gemstone Kingdom|website=www.minerals.net|access-date=2018-05-15}}</ref> Diatomite has multiple industrial uses such as filtering or adsorbing since it has a fine particle size and very porous nature, and gardening to increase water absorption.