#plagioclase

[vigilantsycamore]

LEWD

[sagittariusboyfriend]

oh man oh man i found the most beautiful seam of porphyry (some of it basically glomeroporphyritic) in the dacite-rhyolite mountains behind my parents place! i was out for only two hours and lugged a big heavy piece home with me along with some smaller ones:

look at that huge cryst on the left one.

it has some nice biotite in it as well. it was really fuckin wet (and sweaty!!) though and i just about made it back before it started pouring. looking forward to tomorrow to see how it looks when it dries in the sun

also, looks completely different from the very red dacite (im now thinking that one was more of a rhyolite?) i got from the same area last year, just maybe 100m apart.

the bedrock it came from. look at those three color shifts, left to right, dark to beige to spotted. this is a magma rich in felsic minerals that probably cooled real slow at first, then got mixed up with a mafic one via plate subduction, heated back up and had a big devastating yellowstone-like eruption ~1,9 billion years ago. add some tectonic drift, accretions, isostatic rebound, then some magma intrusions.

[justbegneiss]

Plagioclase and Pigeonite Patterns!!!

A very fun lab today, looking how to determine the anorthite content of plagioclse. Plagioclase often shows with Albite Twinning (which is the characteristic alternating stripes we can see below in the first picture). When we turn the slide, these reverse (black becomes white). In between, theres an intermediate stage where the mineral is all the same colour, usually pale grey; this can be seen in the second picture bottom right. By measuring the difference in angle (approx 4-5°) when different sections go extinct (ie totally black) we can figure out the percentage of anorthite.

[mineralsandsomerocks]

Thin Section viewed in Crossed Polarized Light containing Plagioclase with polysynthetic twins

[geo-bugs]

This is a thin section photomicrograph of one of the lunar mare basalts that was sampled on the Apollo 12 mission. Notice the high olivine content! You can discover some more about this sample by using its identifier, located in the top left corner. Enjoy!

(Let me know if you’d like to see an annotated version)!

Also- quick revision- the field of view is actually 1 mm.

ROCK ON!

[Photomicrograph Credit: Me]

~ :) ~

[geologyjohnson]

View this post on Instagram

Check out the size of these shiny #muscovite crystals on this bit of #pegmatite that @sara_lil_plants brought back from the #cairngorms! Pegmatites are #granite that form during continental collision that unusually large #crystals. The rest of this sample is made of #orthoclase and #plagioclase #feldspar and #quartz. #GeologyJohnson #geology #geologist #igneous #scotland #highlands #scotishgeology #highlandgeology #crystallove #crystalhealing #rock #rocks #rockhound https://www.instagram.com/p/CFB7uJZJBkm/?igshid=srheqsj9l6k4

[earthstory]

Crystal Mush

This is a common texture in igneous rocks – a porphyritic texture. This term refers to igneous rocks that have a population of large crystals surrounded by a fine-grained groundmass or matrix.

A porphyritic texture is produced naturally as magmas cool. A magma is a complicated, multi-component solution – a single molten rock can be composed of 10 different abundant elements. When magma cools, some of these elements start forming minerals, crystallizing out of the melt while other elements remain left behind.

A porphyritic texture therefore is created when some minerals crystallize at higher temperatures than the rest of the magma, forming large crystals surrounded by a groundmass. These larger crystals are plagioclase floating in a groundmass that contains other elements – the photographer labels the rock as an andesite. This type of rock is one way that molten rock can look when it sits inside a “magma chamber”.

The term “magma chamber” probably makes most people picture a big hole in the ground filled with molten rock, but that’s not how the world works. The Earth’s crust is pretty cold, so when molten rock gets into the crust it starts to cool off and crystallize. Most magma chambers aren’t big pockets of molten rock, they’re a mush, filled with a mixture of crystals and molten rock in-between. They’re much more like this rock, a porphyry.

Although we can’t see individual crystals until they reach the surface, scientists have tools that can characterize these mixtures; geophysics. Seismic waves, for example, will travel through just about anything. If a melt is present, even a tiny bit of melt in-between larger grains, seismic waves will travel through that rock and interact with the melt. The presence of a tiny bit of melt therefore can be detected using seismic waves, and that technique has been used to measure the volume and crystallinity of the magma plumbing system beneath many volcanoes around the world. 

-JBB

Image credit: Richard Droker (Creative Commons Licensed)

https://flic.kr/p/6Litaw

[guanimo]

Wurtzite & plagioclase

(wurtzite is a fusion of steven,pearl,amethyst and ruby WITHOUT sapphire) & (plagioclase is a fusion of steven,pearl,amethyst and sapphire WITHOUT ruby) basically the goal was to make wurtzite be the light,fire & magma as plagioclase is more of the cold stone.