Periodic Minerals: Realgar

Realgar (red) with quartz and pyrite.

I was thinking of periodically posting about some particular mineral, fossil, or rock (particularly when I don't have a topic to discuss), and I thought that realgar would make for a good mineral to discuss. Realgar is an arsenic sulfide mineral with the best chemical formula I've ever seen: AsS (sometimes written As4S4). It's very soft (hardness 1.5-2) with a brilliant red color and a resinous, greasy luster and is associated with hydrothermal ore deposits. Several fantastic specimens of realgar come from Paloma, Peru (such as the one pictured).

Interestingly, realgar reacts to sunlight. I don't understand exactly how this happens, but given some time in sunlight, it will alter to a yellow-orange mineral called pararealgar. So, if you collect a sample of realgar, keep it in a dark box or drawer. I didn't know about this when I got my sample (pictured), but I've been fortunate to not have enough space to display my collection and have kept it in a dark drawer. Although it contains arsenic (I don't advise licking it), realgar & pararealgar have been historically used as orange pigments in paints, as well as an ancient pest control chemical.

Comments

Post a Comment

Popular posts from this blog

The Arkansas Paleozoic Stratigraphy Database is live!

Image
A new project I've been working on is now on the blog: the Arkansas Paleozoic Stratigraphy Database . This is a searchable database of the Paleozoic lithostratigraphic nomenclature in Arkansas with some related information. Within this database, you can search for stratigraphic names that not only are currently in use, but names that are now abandoned and replaced, as well as some that have recently been proposed. For each name you can find its age, any sub-divisions, proper usage as used by the USGS and AGS, historical usage (including past and present names), type locality or type area, type section location (if available), primary reference section location (if available), geographic distribution, etymology of the name, and citation of the original publication the name was used in. Also included for each name is a downloadable stratigraphic chart (PDF file) of either the Ozark or Ouachita/Arkansas River Valley region (whichever the unit is best exposed in) that illustrates the s
Read more

Microscopic Meteorites Are All Around Us

Image
Various types of micrometeorites (credit: ©  Jon Larsen ) In 1970, a machine was rigged onto a high-altitude atmospheric balloon and sent 21.7 miles (35 km) into the sky over Texas. The machine, lovingly named the Vacuum Monster after a creature in The Beatles' Yellow Submarine  movie, collected microscopic particles as small as two micrometers (microns) in diameter. Some of which were determined to be extraterrestrial, marking this as the first time "space dust", or more precisely, micrometeorites, were collected at altitude. Micrometeorites are a niche area of study within astrogeology (the study of the geology of extraterrestrial bodies), but has recently been expanding as it is now more accessible for researchers. On a large scale, international space agencies have devoted funding for missions to collect material directly from asteroids and comets, such as the ongoing  Hayabusa 2  mission to the asteroid  Ryugu , which has very recently completed its sampling g
Read more

Naturally Historical Coins from the UK

Image
Just recently, I found out that The Royal Mint of the United Kingdom is releasing three versions of a newly designed 50 pence coin. These coins celebrate the grandmother of paleontology, Mary Anning. Coincidentally, Anning is the focus of a new film, "Ammonite" also (full disclosure: I've yet to see the film, but it seems to be loosely based on Anning's life, much of which is unknown to us today, particularly her romantic life). These coins bear the illustrations of an two marine reptiles, a Plesiosaurus and an icthyosaur called Temnodontosaurus, and a flying reptile called Dimorphodon. All three lived during the Jurassic Period and were discovered by Anning in the early 1800s. The Royal Mint even offers color imbued and gold versions of these coins for a higher price. After finding out about the Mary Anning coins, I immediately found out that The Royal Mint had also produced three versions of the 50 pence coin featuring dinosaurs in 2019! I immediately opened my wall
Read more