Feb 20, 2020
okay, but hear me out. ultramafic rocks.
to anyone who ever said rocks aren’t cool, you’re wrong
seen from Netherlands
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seen from Netherlands
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seen from United States
seen from United States
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seen from Australia
seen from Netherlands
seen from Canada
seen from United States
seen from Netherlands
seen from Canada
seen from Malaysia
seen from Malaysia
seen from Canada
okay, but hear me out. ultramafic rocks.
to anyone who ever said rocks aren’t cool, you’re wrong
レルゾライト 複輝石橄欖岩 544g 原石 標本 北海道様似町 Lherzolite 9 【サイズ】 約 縦90X横98X高43mm 【重さ】 約544g 【産地】 北海道様似郡様似町幌満 【幌満のレルゾライト】 アポイ岳地域の幌満かんらん岩を代表する岩石で、灰緑色が苦土かんらん石、鮮緑色はクロム透輝石、鶯色が頑火輝石、濃い紫いろはクロムスピネルとなります。 【歴史】 レルゾライトはフランス・ピレネー山脈にあるアルプス型橄欖岩体のレルズ山塊から名付けられました。 月の下部マントルはレルゾライトからなると考えられています。 【特徴】 超塩基性火成岩に分類される橄欖岩の一種で、一般に橄欖石のほかに輝石が伴われており、条件によってはスピネル、ザクロ石、斜長石、角セン石、黒雲母などの鉱物が含まれます。 橄欖石が90％以上で輝石の少ないものをダナイトと呼び、それ以下のものについては斜方輝石の多いものをハルツバージャイト、単斜輝石の多いものをウェーライト、両方とも多いものをレルゾライトと呼びます。 ▲▼写真をタップすると商品が購入できるサイトに移動できます。▼▲ #レルゾライト #複輝石 #橄欖岩 #Lherzolite #鉱物 #鉱物標本 #天然石 #天然石ショップ #パワーストーン #パワーストーンショップ #日本産 #国産 #原石 #鉱石 #標本 #japanmineral #mineral #minerals #mineralspecimen #mineralspecimens https://www.instagram.com/p/Bpf6ppKg0qf/?utm_source=ig_tumblr_share&igshid=16vje62vgdx1z
Garnet Lherzolite, Garnet (pink), olivine and orthopyroxene (deep green), Cr-Diopside (Emerald green). From James St. John.
Lherzolite - abstract art from the depths
What you see on the picture below is a thin section of a peridotite - more specifically lherzolite, due to the presence of both clino- and orthopyroxene - placed between two polarization filters and magnified with a microscope. Each individual grain in this section is about 0.5-1mm in diameter, the thickness of this thin section is 30µm.
So how come it shows such unexpected colors?
The spectrum of colors visible under crossed polarizers is an impression that forms when polarized light enters an anisotropical mineral grain, and then is refracted into two separate light rays, both polarized. This phenomenon is called birefringence. This effect produces interference colors, which is what you can see in the photo. Minerals have different birefringences, which produces different interference colors, and this type of microscopy is therefore a useful tool to determine the composition of a rock.
The peridotite group of igneous rocks is the abundant type of rock in the mantle, and is mostly consisting of olivine (>40%) and pyroxenes. As this type of rock consists of more than 90% of mafic minerals (rich in iron and magnesium), the melting temperature is rather high (>1200°C), and the minerals in peridotites are therefore the first to crystallize in the upper mantle. The crystallized rock in the upper mantle is therefore depleted of minerals with lower melting temperatures - which is one of the things that makes the peridotite group special, along with its beautiful show of interference colors in a polarization microscope and its characteristic green color in hand samples.
AV
Photo: AV (using Nikon D300s + 105mm f/2.8 - photo taken down the tubus after oculars were removed)
Sources:
Minerals and Rocks (R. Wilson) - available for free at bookboon.com
The Solid Earth (C. M. R. Fowler)
Portrait of a Planet (S. Marshak)
Further reading:
More on peridotites: http://www.sandatlas.org/2012/08/peridotite/
More on polarization microscopy: http://www.microscopyu.com/articles/polarized/polarizedintro.html