The Earth Story

Vermont Serpentinite Serpentinite is a common rock on Earth, and probably throughout the solar system. It is a type of metamorphic rock, produced when one of the most common minerals in the planet – olivine – gets exposed to water near the surface of the Earth, which of course happens all the time. A bit of water and a bit of pressure and the mineral structure changes, turning it into a soft, easily deformed rock.

Never seen one like this before

Tourmaline is a boron rich mineral that usually crystallilses into prisms with a rounded triangular cross section in a wide variety of colours, depending on the elements present in its mother ichor at formation (as in the first photo surrounded by mica, measuring 2.6 x 1.5 x 1 cm). Growing mostly in pegmatites, those last fluid rich remnants of magmas (granitic in composition in this case) that have concentrated many rare elements that do not fit into the crystal structure of the common minerals such as feldspar and mica and brought them together into often large specimens.

Here we have an oddity like I have never seen before, born in the pegmatites of Minas Gerais in Brazil. Measuring 5.5 x 4.5 x 3.1 cm. Minute fibrous crystals are growing out from a crystal base, and I’m uncertain whether they formed that way or were transformed by passing mineralised fluids later in the specimen’s journey through geological history, a process known as metasomatism. Either way it gets a wow from me…

Loz

Image credit: 1: Crystal Classics 2: Marco Frigiero

Fibrous Malachite

Rock with some chrysotile asbestos, found in New Jersey while just randomly walking

Asbestos fibers in lung tissue

A select few types of minerals produce thin, microscopic fibers. These minerals occur naturally – weathering of some of the most common minerals on earth produces chrysotile, an asbestiform mineral. In much of the world, these minerals were used for insulation and for strengthening consumer products for decades, but a consequence of that is caught in this photo. When humans are exposed to large enough doses of asbestiform minerals in the air, they begin building up in lung tissue. Some types of asbsetiform minerals may dissolve in human lung fluids over a period of years, but others will not, and once they enter the lungs they become coated in an iron-bearing protein structure. The proteins surrounding the fibers have been stained in this thin section to make them more visible. Once the tissue surrounding the asbestos fibers is damaged, it can begin triggering more serious conditions, including lung cancer and mesothelioma.

-JBB

Image credit: Wellcome images https://flic.kr/p/PzM244

Reference: http://bit.ly/2gNX1bA

Previous posts on Asbestos minerals: https://tmblr.co/Zyv2Js1VWOHga

Tiger’s Eye Quartz

The gold streak in this rock is actually an example of tiger’s eye quartz, a particularly neat structure for that mineral. Tiger’s eye quartz consists of long, fine strands of quartz cemented together into a single mineral. This is an uncommon crystal habit for quartz and classically it is explained as happening because quartz is pseudomorphing another mineral.

Minerals like amphibole minerals commonly grow long, thin fibers – we call those asbestiform minerals (asbestos). If fluids flowed through an amphibole rich rock, there can be a chemical reaction that replaces the amphibole mineral with silica, basically turning the fiber into quartz but without changing the structure. That’s a pseudomorph, one mineral grown in the shape of another that it replaced. Amphibole typically has some iron in it, so the reddish color is probably from some leftover iron, suggested here to be in the form of the mineral limonite

Recently, a paper proposed an alternative explanation – that tigers eye quartz actually grows through fluids that flow in slowly-opening cracks. If the crack opens slowly enough, then the quartz will only grow at the tip where the crack expands, also creating this needle-like structure. At present the literature doesn’t seem clear on which explanation is correct.

Although difficult to demonstrate from a single photo, this type of quartz also shows chatoyancy – the effect where light is focused by fibers into a single bright spot if the angle is right, also known as a Cat’s Eye effect (https://tmblr.co/Zyv2Js1Ek_-NV).

-JBB

Image credit: James St. John https://flic.kr/p/BoEUtx

References: http://www.minerals.net/gemstone/tiger's_eye_gemstone.aspx http://www.mindat.org/min-3960.html

Pele's hair

One of the weirdest forms molten magma takes as it emerges onto the cold surface of the globe and freezes are these thin strands of glass that resemble fur, named after the Hawaiian goddess of smoking mountains. They form in fast moving flows and lava fountains, where the molten rock is stretched or blown by winds and freezes too fast to produce even microscopic crystals, forming an amorphic glass instead. It is light enough for wind transport, and can gather in incongruous places such as treetops and telegraph poles, wherever the breeze wafts.

It forms in runny hot lavas such as basalt, which are fluid enough for stretching due to the low percentage of silica they contain (silica forms polymer like chains in lava making it more viscous, the faster it runs the less it has). It is both brittle and sharp, so care should be taken when handling it since a bunch of needle sharp glass splinters in the hand, even if erupted from the depths of the globe is the last thing most people want when playing with a rock. The usual shade is a golden straw yellow. Maximum length is around 2 metres, though these features are very fragile and rarely survive long. This isn't the only shape that basaltic glass takes, others include Pele's seaweed (http://on.fb.me/1OTTIwd) and a so far unique frozen bubble of volcanic glass with gas inside (see http://on.fb.me/1Q8VcUh).

Loz

Image credit: 1: Cm3826 2: NASA 3: D.W. Peterson http://on.doi.gov/1Q0zWxW

Hair Ice

If you’ve ever had the chance to hike into a boreal forest on a midwinter morning, you might have seen these glistening, filamentous strands in clumps on the forest floor or wrapped round woody branches. These cotton candy-like fibers are “hair ice” — delicate strands of ice that grow from the insides of rotting tree branches. Hair ice is incredibly fine — just 0.01 millimeters in diameter — and forms from water caught inside plant stems as surrounding temperatures fall below freezing point. Because water expands when frozen, the ice crystals are squeezed through the microscopic orifices of its stemmed container, forming the threadlike fibers as seen in the photos below.

Hair ice was first studied by Alfred Wegener (the same Alfred Wegener who proposed the theory of continental drift), and he observed that the ice formed when the mycelium of a fungus was present. The mycelium is the roots of a fungus that wraps around rotting wood in a cocoon-like structure to absorb nutrients. Only recently have researchers have ascertained that the mycelium of certain fungi helps keep the hair ice in place as it grows, and the next step would be to determine the mechanics between the presence of fungi and their influence on hair ice formation.

-DC

Photo credits: http://bit.ly/1E477cH More reading: http://bit.ly/1OJIXJT http://bit.ly/1JGEdpd http://bit.ly/1K0hPmo Watch a time-lapse video of hair ice growing from dead wood: http://bit.ly/1JATNOA

Original sources: http://www.biogeosciences.net/12/4261/2015/bg-12-4261-2015.html http://bit.ly/1LwxCPI

Seraphinite disc

While I covered this lovely green mineral before (see http://on.fb.me/1Hl3vnM), this wonderful 15 cm across natural aggregate of fibrous crystals is a stunner. Formed by the alteration of limestones by hot brines spat out of a cooling iron rich granite that was stewing in its own juices after reaching its buoyancy point in the crust of the Earth in one specific Siberian locality, it was named after the supposedly delicately textured wing feathers of the highest order of angels. The fibres could be cut into catseye stones, but it would ruin a wonderful mineral specimen, something I'm generally against (though for the record, I have nothing against cutting river rolled pebbles and angular cleavage fragments, just lushly formed crystals)

Loz

Image credit: Carion Mineraux

The use of asbestos

Asbestos, described in part one of this series found here: http://tmblr.co/Zyv2Js1VGcU1g, is really a remarkable material. It combines two properties that make it incredibly useful – first, it forms tiny fibers, in some cases even like fibers that we use to fill fabric in heavy jackets or blankets today. Interlocking fibers prevent air from moving rapidly through them, and so fibrous material makes excellent insulation – holding heat on one side and cold on the other.

In that sense, asbestos minerals are no different than any other set of insulating fibers, but what makes them unique is they’re also rocks. If you take a flame to the insulation in a blanket or a jacket, either the material is going to melt or its going to catch on fire – the fibers are organic and will burn in the air (The Earth Story advises you not to actually try this). If instead you try to light a rock on fire…well you won’t get very far. Trying to light asbestos on fire is literally trying to light a rock on fire – it will not ignite.

Asbestos fibers, therefore, were hugely useful. They were abundant, easily mined around the world, could be moved and sprayed onto surfaces at low cost, were solid and could even be used in building material, and they did an incredible job keeping heat out.

For these reasons, it seems to make sense that as buildings began growing larger, people began insulating them with asbestos. The same way that other insulating substances are used to keep heat from escaping though attics and windows today, asbestos fibers were commonly used a century ago, but with the added benefit that the insulation was completely fireproof.

Coating steam pipes to keep them from losing heat or coating walls to keep heat out is enormously important, and if the material isn’t fireproof, a small fire will be able to rapidly expand. Asbestos is a rock and rocks don’t burn, so if asbestos is used for insulation, the fact that it doesn’t burn can literally help save lives.

  The fibrous property of asbestos, particularly chrysotile asbestos, even gave it other uses –you could actually sew the material together and make fabrics. These gloves? Actually made from asbestos. They give all the properties of rocks – incredibly insulating and virtually fireproof, and are even wearable.

Perhaps the greatest example of this usage was on naval vessels. Insulating these ships to be able to move heat or steam around was obviously important, and those ships contained large amounts of explosives. Keeping fires on ships from expanding and reaching the magazines literally would save lives, and asbestos did that.

It is genuinely no exaggeration to say that there are people who survived the Second World War who would not have survived without asbestos.

Asbestos usage began phasing out in the decades after the war but the first replacement materials were no where near as good in these qualities – it took decades to develop replacements as good as asbestos, and I would bet that on several properties asbestos still rivals the best options available today.

If you’ve ever wondered why the hallways of old buildings are full of asbestos and why people need to be careful while working on them, this is why asbestos was so widely used. These usages are why these minerals spread around the world, why they were used in millions of places, and why the health issues became so widespread.

-JBB

Image credits: http://www.tradeindia.com/fp410797/Asbestos-Glove.html http://www.maine.gov/dep/waste/asbestos/photogallery.html http://upload.wikimedia.org/wikipedia/commons/b/b7/Asbestos_fibres.jpg

Read more: http://bit.ly/1zMddjv

What is Asbestos? If you’re like many of the students I’ve had in class, you’ve heard of asbestos thanks to either ads on television for law offices who process asbestos-related claims or through warning labels on big plastic sheets that appear in the hallways whenever work is being done in an old university building. For many people, asbestos is simply “bad”; something to be avoided at all costs.  This series of posts will describe asbestos, what it was use used for and why, and what it does to people. For anyone who reads these who was actually harmed by asbestos…please bear with me, I promise this series will cover your issues fairly. From a geologists perspective, asbestos isn’t even a single mineral, it’s a mineral “habit”, a shape taken by a class of minerals. This mineral habit is defined by fibers like those seen in this electron microscope image; tiny mineral fragments that are long in one direction, but are usually so tiny that the human eye has a tough time seeing them. Asbestos minerals are silicates, the most common mineral class on earth, built around the backbone of the silicon-oxygen bond, but with 2 possible different arrangements, each from a different mineral group. The first of these minerals, amphiboles, are double-chain silicates, and their molecular structure is outlined in the second image. Amphiboles are built by a series of 4 silica tetrahedra (with the silicon atom at the center surrounded by 4 oxygen atoms) that share oxygen atoms at their corners and extend in one direction. To balance the charges, these silicate backbones hold metal ions such as calcium, iron, and magnesium, at various points in their structure. The bonds between silicon atoms are extremely strong and hard to break, while the bonds between silica and metal are weaker. Amphiboles often break into elongate needles, with their shape controlled by the patterns between those strong and weak bonds. Not every amphibole mineral forms fibers– many form larger crystals, but there are 5 different minerals which do: amosite, crocidolite, anthophyllite, tremolite, and actinolite. Each of those minerals has the same basic structure but different ions in it, causing different colors, slightly different fiber shapes, and even different levels of harm to humans. The other type of asbestos, chrysotile, is a totally different type of mineral known as a serpentine. Serpentine minerals are silicates that form when mafic rocks like those from Earth’s mantle are exposed to water and chemically weathered. The atomic structures reorganize from the initial mineral form and begin including water molecules, creating alternating sheets of silicon atoms, oxygen atoms, and water-rich layers. Chrysotile asbestos does something really weird. See the flat sheet illustrated in the diagram? Imagine bending that sheet around itself into a tube, like a piece of paper. That’s exactly how chrysotile asbestos forms fibers; the sheets bend around and bond into a single tube, creating a structure strong in one direction and completely isolated in the others.  These two types of minerals often form in similar environments – through the interaction of rocks and water, so it isn’t uncommon to find them together. They form large deposits, able to be mined in huge quantities. They even outcrop at the Earth’s surface and can be walked on or collected as samples. The key feature of asbestiform minerals is that their molecular structure shapes them into fibers, long in one direction and short in the other 2. -JBB Image credits: http://en.wikipedia.org/wiki/Asbestos#mediaviewer/File:Anthophyllite_asbestos_SEM.jpg http://chempaths.chemeddl.org/services/chempaths/?q=book%2FGeneral+Chemistry+Textbook%2F1174%2Fintroduction-ambit-chemistry&title=Using_Crystallography_to_Test_Materials_for_Asbestos http://upload.wikimedia.org/wikipedia/commons/1/16/Blue_asbestos_(teased).jpg