conchoidal

Don’t let obsidian steal your heart!

While this is very unlikely in today’s culture, it was almost a certainty for those individuals sacrificed by the Aztecs during religious rituals. Probably the only consolation for someone who is about to have their heart ripped out is the knowledge that the knife would be sharp. Aztec ceremonial knives were composed of flint or obsidian blades, and it is the geological properties of these rocks that would have at least made your demise swift.

Keep reading

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A curve with polar coordinates,

(1)

studied by the Greek mathematician Nicomedes in about 200 BC, also known as the cochloid. It is the locus of points a fixed distance away from a line as measured along a line from the focus point (MacTutor Archive). Nicomedes recognized the three distinct forms seen in this family for , and . (For , it obviously degenerates to a circle.)

The conchoid of Nicomedes was a favorite with 17th century mathematicians and could be used to solve the problems of cube duplication,angle trisectionheptagon construction, and other Neusis constructions (Johnson 1975).

In Cartesian coordinates, the conchoid of Nicomedes may be written

(2)

or

(3)

The conchoid has  as an asymptote, and the area between either branch and the asymptote is infinite.

This is all according to Wolfram. See Wolfram’s website for more details.

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Amethyst (Quartz)

  • Trigonal crystal habit
  • 7 hardness, but lower in less pure forms
  • Conchoidal (shell-like fracture)
  • 2.65 specific gravity
  • White streak
  • Vitreous luster

Quartz comes from an old German word for ‘hard,’ twarc. It has a ton of different varieties, but amethyst is one of the most well known. It’s also the birthstone for February, which is why I’m posting about it. Amethyst means ‘not intoxicated’ because it used to be believed to protect its wearer from the effects of alcohol. Pure quartz is clear, so amethyst is an impurity caused by traces of radiation that make it purple. Quartz, and therefore amethyst, is a silicate with the chemical composition SiO2. It’s the second most common mineral in the world, after feldspar,and it’s an important component of granite and felsic igneous rocks in general. Quartz is common in sedimentary rocks, and present in carbonates and metamorphic rocks. It generally crystallizes from magma,and the largest crystal of quartz measures about 6 by 1.5 by 1.5 meters and was found in Brazil. Pliny the Elder actually believed quartz crystals were ice, frozen for a very long time. 

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Benitoite

  • Hexagonal structure
  • 6-6.5 hardness 
  • Conchoidal fracture 
  • White streak 
  • 3.6 specific gravity
  • Vitreous luster 

 Benitoite, named for its occurrence near the San Benito River in California, is an extremely rare barium titanium silicate (BaTiSi3O9). It occurs in Japan, Arkansas, and California, but the only gemstone quality rocks come from California, where it was first discovered. More specifically, it’s found in natrolite veins in California. Benitoite is basically hydrothermally altered serpentinite, so it’s usually found with serpentinite. What makes benitoite unique is that it fluoresces under UV light; usually in the spectrum of bright blue to white-blue. Benitoite is usually blue or clear, and is already rare, but a certain rarer clear variety fluoresces red under long wave UV light. Thank you so much to the anon for the submission! I’m almost to 100 followers and I had no idea people would like rocks as much as I do. Thanks so much!