Chert – the birthstone of our species

Few varieties of stone have as lengthy lasting and intimate relationship with our species as do these of the chert household.  People have been utilizing this difficult, glassy stone repeatedly to make instruments for the reason that time of Homo habilis, some 1.5-2 million years in the past.  Our neolithic ancestors mined chert utilizing hearth to crack the stone (see video to see the way it was finished), no less than 33,000 years in the past on the Nazlet Khater web site in Egypt chert was extracted from subterranean mines,  and flint (a kind of chert) was used earlier than we had matches to make hearth, as we speak we use crushed chert because the abrasive on some sandpapers, and to extract exquisitely detailed micro-fossils from the distant previous.  Once I labored as an archaeologist close to Santa Barbara a lot of the projectile factors, stone awls, and chopping instruments we discovered had been made out of chert.

What is that this “chert” now we have been utilizing so assiduously for the final 2 million years?

Chert is a microcrystalline stone fabricated from silicon dioxide (SiO2) with a cryptocrystalline construction (crystals so wonderful that they’re troublesome to see even below a microscope) that lacks cleavage planes.  One of the crucial helpful, for us, facets of cryptocrystalline supplies resembling chert is that when they’re struck they shatter in a predictable conical method (conchoidal fracturing).  Obsidian and plate glass share this attribute, making them and chert wonderful for making extraordinarily sharp stone instruments.  Chert is extra frequent than obsidian, however nonetheless uncommon sufficient that it was traded over nice distances.  One other useful side of chert is that this can be very exhausting, raking a 7 on the Mohs scale.

Various well-known minerals fall into the chert class: flint, jasper, radiolarite, chalcedony, agate,  and onyx are all varieties of chert, every with particular traits that give them sufficient distinction from one another to warrant particular names.  The well-known (and costly) sharpening stones from Arkansas are made out of novaculite, a porous, metamorphosed chert that makes a wonderful abrasive.  Flints are typically top quality cherts which are discovered particularly in chalk or limestone; these are deposited diagenically (through silicon alternative).  Chalcedony, agate, and onyx are a nested subset of minerals with chalcedony, a fibrous type of chert, being the mother or father of the group.  Jasper is normally present in affiliation with volcanic exercise and is usually thought-about to be below the chalcedony subset.  Jasper, agate, and onyx are in style semi-precious stones used for jewellery and generally intricately carved.

Jasper cameo pistrucci - Chert – the birthstone of our species

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Crimson jasper cameo of Medusa by Benedetto Pistrucci (supply)

What obtained me began interested by cherts as soon as extra was a brief day-hike I took with a pal within the Marin Headlands, these steep sided hills to the north of San Francisco which are so typically obscured by the thick maritime fog.

Marin Headlands and the Golden Gate bridge partially hidden by fog

Marin Headlands and the Golden Gate bridge partially hidden by fog

The Northern California coast has a posh geology and is present process a variety of divergent modifications concurrently.  That is an emergent shoreline (Geology of Northern California chapter 10, web page 37), a spot the place the land is slowly rising in elevation.  Rising lands typically undergo from excessive charges of abrasion and the California coast has an much more drastic set of things contributing to the erosion uncommon than merely rising land.  The bedrock is fractured by many faults, weakening the stone, earthquakes (most extraordinarily minor) shake rubble free periodically, and each wind and water eat away on the ocean dealing with slopes.  As well as, the ocean degree has risen a number of hundred toes for the reason that final glaciation twelve thousand years in the past, and the surf is greedily pounding on the hills, tearing components of them away.

Should you watched the video you in all probability observed that the chert they had been mining peeled off in plates, certainly that the entire formation was made up of sheets of stone layered atop one another like pastry dough.  About 50% of rock within the Marin Headlands is chert and has the same texture.

Radiolarin ribbon chert cliff showing soft folds and a sharp fault-line cut

Radiolarite chert cliff displaying tender folds and a pointy fault-line reduce

That is ribbon chert, extra formally generally known as radiolarite chert.  It will get the latter identify as a result of it’s a biogenic stone made out of the semi-gelled skeletons of radiolaria, a kind of plankton that builds a silica based mostly assist construction.  These this rock was laid down over a 100 million yr span starting 200 million years in the past and is stuffed with tiny fossils of the radiolaria.  Supposedly a few of these are giant sufficient to see with a regular hand-lens.

The folding tells us one thing fascinating.  The folds within the above photograph are clean, which means that this in all probability slumped slowly whereas it was nonetheless ductile.  Parts of the cliff have sharp folds the place the rock broke, indicating that these deformations more than likely occurred extra quickly and after the stone had misplaced a lot of its ductility.

Red and greenish/blue indicate iron, either in oxodised or reduced form

Crimson and greenish/blue point out iron, both in oxidised or decreased kind

A lot of the chert right here is purple, however there are lots of patches of vibrant blue-green and aqua as properly.  The colours in chert point out hint quantities of different minerals.  The purple and the stunning greenish-blue are each indicators of iron, the purple indicating that the iron has oxidised, the blue-green that it has been decreased (had the oxygen faraway from it).  That is just like the mottled gleying that one sees in wetland clay soils.  I’m notably keen on the blue and inexperienced colours in chert, maybe as a result of they’re a bit extra uncommon than the purple.

Close-up of blue/green chert bands

Shut-up of blue/inexperienced chert bands

The hardness of the chert results in seashores with an fascinating texture of sand, extra like tiny shiny pebbles than the usual sand.

Chert sand

Chert sand

The mix of colours on the cliffs, seashore, sky, and ocean make for a pleasant mixture as properly.

Tennessee Valley beach in the Marin Headlands

Tennessee Valley seashore within the Marin Headlands

Now we have been utilizing chert for almost so long as now we have been utilizing instruments, near 2 million years now with no signal of slowing down.  If our species had a birthstone it could in all probability be chert.

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Molly Kozlowski

立中式速繪 動態姿勢繪圖技巧 ポーズが描ければ 動きも描ける たてなか流クイックスケッチ

作者: 立中順平  
出版社:楓書坊 |譯者: 游若琪
規格:平裝 / 217頁 / 19 x 25.7 x 1.08 cm / 普通級 / 部份全彩 / 初版
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  ➊ 建立正確的心態
  ➋ 練習簡單畫全身的速繪技巧▁▁火柴人練習
  ⑴ 將全身分成15個部位,
  「頭 部、胸部、骨盤」是橢圓形。
  ⑵ 注意基本結構,不要注意輪廓和細節
  ⑶ 立體化
  ⑷ 創造不對稱平衡
  1993年開始在Disney Animation Japan擔任動畫師。
  後來進入Answer Studio,目前是自由工作者。
  曾參與《跳跳虎歷險記》(Disney)、《棒球大聯盟》(電視版)、《鑽石王牌》、《YURI !!!on ICE》、《佐賀偶像是傳奇》等作品。
由曾經在華特迪士尼動畫工作室與日本動畫公司Answer Studio的日本資深動畫師立中順平撰寫的速繪教學書
第一章節:速繪繪畫 P1-73.

Design College students’ Summer season Break

With summer break fast approaching, graphic design students like me are trying to figure out productive ways to spend their time. Work for money? Work for experience? Summer classes?

I’ve spent the past few months doing everything I can to
find an internship this summer. Finding a company that isn’t an MLM and will
actually pay good money for your design work is tough. Luckily, graphic design
is a field that’s in demand, so there are a lot of good options out there.

The other option for getting design experience during the summer
break is freelance work, but that comes with its own slew of issues. There’s
nothing worse than beginning to work with a client and getting excited for a
project just for them to look at you with a face like the Surprised Pikachu Meme
when you start to discuss cost.

With two weeks left in the semester, here’s hoping we figure
something out soon!