Crystal of the Day for August 6 – Pyrite (Fool’s Gold)



The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral’s metallic luster and pale brass-yellow hue have earned it the nickname fool’s gold because of its resemblance to gold. The color has also led to the nicknames brass, brazzle and Brazil, primarily used to refer to pyrite found in coal.

Pyrite is the most common of the sulfide minerals. The name pyrite is derived from the Greek πυρίτης (puritēs), “of fire” or “in fire”, in turn from πύρ (pur), “fire”.In ancient Roman times, this name was applied to several types of stone that would create sparks when struck against steel; Pliny the Elder described one of them as being brassy, almost certainly a reference to what we now call pyrite. By Georgius Agricola’s time, the term had become a generic term for all of the sulfide minerals.

Pyrite is usually found associated with other sulfides or oxides in quartz veins, sedimentary rock, and metamorphic rock, as well as in coal beds, and as a replacement mineral in fossils. Despite being nicknamed fool’s gold, pyrite is sometimes found in association with small quantities of gold. Gold and arsenic occur as a coupled substitution in the pyrite structure. In the Carlin–type gold deposits, arsenian pyrite contains up to 0.37 wt% gold.

Uses of Fool’s Gold

Pyrite enjoyed brief popularity in the 16th and 17th centuries as a source of ignition in early firearms, most notably the wheellock, where the cock held a lump of pyrite against a circular file to strike the sparks needed to fire the gun.

Pyrite has been used since classical times to manufacture copperas, that is, iron(II) sulfate. Iron pyrite was heaped up and allowed to weather as described above (an early form of heap leaching). The acidic runoff from the heap was then boiled with iron to produce iron sulfate. In the 15th century, such leaching began to replace the burning of sulfur as a source of sulfuric acid. By the 19th century, it had become the dominant method.

Pyrite remains in commercial use for the production of sulfur dioxide, for use in such applications as the paper industry, and in the manufacture of sulfuric acid. Thermal decomposition of pyrite into FeS (iron(II) sulfide) and elemental sulfur starts at 550 °C; at around 700 °C pS2 is about 1 atm.

Pyrite is a semiconductor material with band gap of 0.95 eV.

During the early years of the 20th century, pyrite was used as a mineral detector in radio receivers, and is still used by ‘crystal radio’ hobbyists. Until the vacuum tube matured, the crystal detector was the most sensitive and dependable detector available- with considerable variation between mineral types and even individual samples within a particular type of mineral. Pyrite detectors occupied a midway point between galena detectors and the more mechanically complicated perikon mineral pairs. Pyrite detectors can be as sensitive as a modern 1N34A diode detector.

Pyrite has been proposed as an abundant, inexpensive material in low cost photovoltaic solar panels. Synthetic iron sulfide is used with copper sulfide to create the experimental photovoltaic material.

Pyrite is used to make marcasite jewelry (incorrectly termed marcasite). Marcasite jewelry, made from small faceted pieces of pyrite, often set in silver, was popular in the Victorian era.


Astronomy Picture of the Day – In the Shadow of Saturn’s Rings

Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2012 July 3

In the Shadow of Saturn’s Rings 

 Image Credit: NASA/JPL-Caltech/Space Science Institute/J. Major

 Explanation: Humanity’s  robot orbiting Saturn has recorded yet another amazing view. That robot, of course, is the  spacecraft Cassini, while the new amazing view includes a  bright moon,  thin rings,  oddly broken clouds, and  warped shadows. Titan, Saturn’s largest moon, appears above as a featureless tan as it is continually shrouded in thick clouds. The rings of Saturn are seen as a thin line because they are so flat and imaged nearly edge on. Details of Saturn’s rings are therefore best visible in the  dark ring shadows seen across the giant planet’s cloud tops. Since the ring  particles orbit in the same plane as Titan, they appear to skewer the foreground moon. In the upper hemisphere of Saturn, the clouds show many details, including  dips in long bright bands  indicating disturbances in a high altitude jet stream. Recent precise measurements of how much Titan  flexes as it orbits Saturn hint that  vast oceans of water might exist deep underground.

Astronomy Pic for June 19th – NuSTAR X-Ray Telescope

Discover the cosmos!Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2012 June 19

NuSTAR X-Ray Telescope Launched Illustration

 Credit & Copyright: Fiona Harrison et al.CaltechNASA


 Explanation: What’s left after a star explodes? To help find out, NASA  launched the  Nuclear Spectroscopic Telescope Array (NuSTAR) satellite into Earth orbit last week. NuSTAR’s ability to focus hard  X-rays emitted from the nuclei of atoms will be used, among other things, to inspect the surroundings of  supernova remnants so as to better understand why these supernovas occurred,  what types of objects resulted, and what mechanisms make their surroundings glow so hot. NuSTAR will also give humanity   unprecedented looks at the  hot corona of our Sun, hot gasses in  clusters of galaxies, and the  supermassive black hole in the  center of our Galaxy. Pictured above is an artist’s illustration depicting how  NuSTAR works. X-rays similar to those used in your dentist’s office enter the telescope on the right and  skip off two sets of  parallel mirrors that focus them onto the detectors on the left. A long but low-weight mast separates the two, and the  whole thing is powered by solar panels on the upper left. Part of the excitement involving  NuSTAR is not only what things it is expected to see, but by  looking at the universe in a new way, what things that are completely unknown  that might be discovered. NuSTAR has a planned two year lifetime.

NASA’s Voyager 1 spacecraft nears interstellar space

The probe is encountering 25 percent more cosmic radiation as it pushes over 11.1 billion miles from Earth, indicating that it is reaching new regions of space.


NASA’s Voyager 1 spacecraft has encountered a new environment more than 11 billion miles from Earth, suggesting that the venerable probe is on the cusp of leaving the

solar system.

The Voyager 1 probe has entered a region of space with a markedly higher flow of charged particles from beyond our solar system, researchers said. Mission scientists suspect this increased flow indicates that the spacecraft — currently 11.1 billion miles (17.8 billion kilometers) from its home planet — may be poised to cross the boundary into interstellar space.

“The laws of physics say that someday Voyager will become the first human-made object to enter interstellar space, but we still do not know exactly when that someday will be,” said Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena, in a statement.

“The latest data indicate that we are clearly in a new region where things are changing more quickly,” Stone added. “It is very exciting. We are approaching the solar system’s frontier.”

Far-flung spacecraft


Voyager 1 and its twin, Voyager 2, launched in 1977, tasked chiefly with studying Saturn, Jupiter and the gas giants’ moons. The two spacecraft made many interesting discoveries about these far-flung bodies, and then they just kept going, checking out Uranus and Neptune on their way toward interstellar space.

They’re not quite out of the solar system yet, however. Both are still within a huge bubble called the heliosphere, which is made of solar plasma and solar magnetic fields. This gigantic structure is about three times wider than the orbit of Pluto, researchers have said.

Specifically, the Voyagers are plying the heliosphere’s outer shell, a turbulent region called the heliosheath. But Voyager 1’s new measurements — of fast-moving galactic cosmic rays hurled our way by star explosions — suggest the probe may be nearing the heliosphere’s edge.

“From January 2009 to January 2012, there had been a gradual increase of about 25 percent in the amount of galactic cosmic rays Voyager was encountering,” Stone said. “More recently, we have seen very rapid escalation in that part of the energy spectrum. Beginning on May 7, the cosmic ray hits have increased five percent in a week and nine percent in a month.”

More measurements needed


While it may be tough to identify the moment when Voyager 1 finally pops free into interstellar space, scientists are keeping an eye on the cosmic ray measurements and a few other possible indicators.

One is the intensity of energetic particles generated inside the heliosphere. Voyager 1 has recorded a gradual decline in these particles as it flies farther and farther away from Earth, but it hasn’t seen the dramatic dropoff that scientists expect would accompany an exit from the solar system.

The Voyager team also thinks the magnetic fields surrounding the spacecraft should change when it crosses the solar boundary. Those field lines run roughly east-west within the heliosphere, and researchers predict they’ll shift to a more north-south orientation in interstellar space. They’re currently looking at Voyager 1 data for any signs of such a transition.

In the meantime, both Voyagers just keep on flying and exploring. Voyager 2 trails its twin a little bit; it’s currently 9.1 billion miles (14.7 billion km) from home.

“When the Voyagers launched in 1977, the space age was all of 20 years old,” Stone said. “Many of us on the team dreamed of reaching interstellar space, but we really had no way of knowing how long a journey it would be — or if these two vehicles that we invested so much time and energy in would operate long enough to reach it.”

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