The Earth Story

Staurolite

Usually found as red to brown prismatic crystals, the iron aluminium oxide mineral staurolite is very useful to metamorphic geologists, since it is fairly common and records the pressure and temperature of mineral transformation undergone in the bowels of the Earth by the precursor rocks (called protoliths). Indicating the metamorphic grade known as amphibolite facies, it commonly occurs in transformed mudstones and often forms a variety of beautifully twinned crystals such as this natural cross.

The name comes from the Greek word for cross, and the twins are two crystals that have grown together interpenetrating each other at either 60 or 90 degrees. It has been a good luck charm for Christians since antiquity, and was known in olden days as fairy stone. Nowadays it is also the state mineral of Georgia (USA). It commonly occurs associated with garnet, kyanite and micas in regional metamorphic (i.e. wide scale) schists.

Our past posts on twinned crystals: http://tinyurl.com/mvbojujhttp://tinyurl.com/l8yba54, http://tinyurl.com/ntdtdb6, http://tinyurl.com/nr7cq6n, http://tinyurl.com/kp6nluf and http://tinyurl.com/nr7cq6n

Loz

Image credit: Mineral Auctions http://www.mindat.org/min-3753.html

The Cathedral Window An amazing black opal from Lightning Ridge in Australia displaying harlequin pattern (named after the costume of a character in French carnival mystery plays). It weighs in at nearly 9 carats and measures 15x13mm. It recently sold at Bonhams for a ridiculous sum. Loz Image credit: Bonhams Auction House http://www.bonhams.com/auctions/21032/lot/1398/

The most barren place on earth…

On Friday night I posted an image of a lonely road in Death Valley (http://tinyurl.com/kdvl3gs). It just seemed like a good time for it…but some of the comments correctly pointed out that Death Valley is not as barren as one might think. Life finds many niches even in harsh climates, whether it is just microbial life or life that is ephemeral, only existing at certain times of the year.

To start a new week, I bring you a photo of the area well known as the most barren place on Earth. This photo comes from the Atacama desert of Chile, the location that, on average, has the least amount of life per area on Earth. It is used as an example of an area so barren that it might be comparable to Mars.

This desert is a thin strip of land, 1000 kilometers long, sandwiched between the Andes Mountains and the Pacific Ocean

There are areas in this desert that have never received rain in recorded history. Only a few human settlements exist in the areas where there is a stable supply of water.

So…I ended the week with one barren desert…here’s a slightly different version of a barren, lifeless desert to start off the week. Somehow, this kind of barren desert seems like a good, cheerful way to start a new week.

-JBB Image credit: Yamil Hussein (Creative Commons share) http://www.fotopedia.com/items/dcqlqtt0d4eht-ACQSXt2wEKM

Sunday morning sunrise in the Alps

Standard Sunday Icelandic River.

Sea otter sunday

About as good of a sunday morning sunrise as I can give you.

Good morning world

The meaning of black

Unless they are volcanic basalts, black rocks tend to mean one thing to a geologist: an absence of rotting, and quite often a hard time for life. It denotes a period where the ground or sea bottom was poor in oxygen, as happens in the current day in peat bogs, some deltas where sediments bury the organic matter quickly or in stratified lakes or basins such as the Black Sea. When organic matter does not rot, it leaves a black carbon rich residue behind, giving a colour to the surrounding rocks. When metamorphosed during a continental collision the carbon turns into graphite, often woven through the texture of the rock.

The most common black rocks are mudstones, sometimes extremely localised, that are born in lakes or seas. Oil shales are the most organic rich examples and provde the source material for the oil trapped elsewhere in the sedimentary stack, or even directly from the shale itself these days. The vast oil deposits in the limestones of the Middle East come from a series of Cretaceous events (145-65 million years ago) when the Tethys Ocean became stratified and the sea bottom was anoxic. The dark strata in the photo are coal seams from the Alaska range. Coal often forms in deltas and peat bogs, where organic matter is either buried away from oxygen by rapid sedimentation or does not rot due to the anoxic and acidic conditions in the bog.

Loz

Image credit: Liyamu

How's this for a view Tungurahua spouting provides a perfect backdrop for a pleasant Sunday activity over in Ecuador. Very active, it has been waking and dozing since 1999, producing explosive and smoky silica rich lavas. Named using the Quechua word for throat of fire, we reported on its recent activity at http://tinyurl.com/l9kpcnc,http://tinyurl.com/oso3jmo andhttp://tinyurl.com/kqerdss Loz Image credit: Caters News Agency