The World’s Top Five Diamonds




How would you choose the world’s top five diamonds? By cost? Carat? Who owns them?

People occasionally pay insanely high prices for some unique stone, but a diamond’s monetary value depends on social factors that change over time.

That’s why you can’t go by price. Wealthy people certainly pay for excellent quality, but they also buy gems to impress other people or to fulfill some other inner need; or to possess something that was once owned by somebody they admire; or for historic value; or for a multitude of other reasons.

Jewelers, of course, cater to social factors, but at the business level they have to judge a diamond objectively. They go by:

  • Its chemical structure (type)
  • Internal and external imperfections (clarity)
  • Its hue, tone, and saturation (color)
  • How well it was cut into a gem (cut)
  • Its weight (carat)
  • Most of us know something about the 4 C’s – clarity, color, cut and size. What is diamond type all about?
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Philae Has Landed on Comet 67P!

Update, November 14, 4:48 p.m. Pacific: Philae is in a location that doesn’t get enough sunlight to operate its solar panels. It is running on the power it left Rosetta with. The ESA has put it to sleep after getting as much science out of it today that they could. It can be woken up as needed (hopefully). Emily Lakdawalla of the Planetary Society has more about this.

Bouncing…who would have expected it to do that on a comet!

Update, November 13, 5:08 p.m. Pacific: Philae bounced three times during landing yesterday (a surface quality they didn’t expect the comet to have, it seems), and while Rosetta still can’t see it, per news reports, the lander is now in a depression near a cliff. There isn’t enough sunlight to power its solar panels, reportedly, and one leg is off the ground.


The ESA team may have decided to use the MUPUS instruments to move the lander – time will tell on that.

They deduced this from instrument readings, I guess, and this imagery from Philae:



Last image of Philae taken from Rosetta, a few minutes after separation.  ESA

Last image of Philae taken from Rosetta, a few minutes after separation. ESA

Here’s an ESA news release. So far, there are two tweets from Philae’s team:

Wow! Just…wow!



And there is this…location to be determined later:


And this…

Rosetta Comet Landing Livestream


Mission control for Rosetta and Philae.  ESA

Mission control for Rosetta and Philae. ESA

We’re doing this week’s Ad Astra post early because the European Space Agency is sending down the Rosetta mission’s Philae lander on Wednesday, November 12.

It’s going to attempt a landing on Comet 67P, according to the present schedule, at around 10:35 a.m. Eastern. Since there is a time delay due to distance (this is happening about midway between Mars and the asteroid belt), people on Earth won’t know if it worked until about a half-hour later.

No one knows what a comet’s surface is like, so we’ll all have to wait and see what happens.

The Livestream will be here, starting Tuesday. The ESA will have its webcast here, also starting Tuesday. NASA-TV will carry live coverage here from 9 to 10 a.m. Eastern on Wednesday and then will switch over to ESA coverage from 10 to 11:30.

Why Clay Makes Good Ceramics


These two things have ceramics in common, even though they are separated in time by 5,500 years.  Valdivia figurine and Space Shuttle

These two things have ceramics in common, even though they are separated in time by 5,500 years. Valdivia figurine and Space Shuttle

People have been using clay since the Stone Age, but what exactly is it? Why does clay make such good ceramics?

What is clay?

Clay forms wherever rocks that contain aluminum and silica are exposed to air, water, or steam. It’s all over the place, in other words – from mountains through volcanoes and geothermal fields to the ocean floor – and usually mixed in with a lot of other organic and inorganic stuff.

Not surprisingly, clay doesn’t have a single chemical formula. It is defined by its physical properties, and you can easily guess what these are. Clay absorbs or loses water easily, for instance, and it swells when wet.

Here are the two key properties of the clay group of minerals when it comes to ceramics:

  • They’re soft and made of tiny crystals (less than 0.004 mm in size) that are arranged in sheets
  • Some are plastic when mixed with a little water – you can deform them and they will hold the new shape

That plasticity, of course, is why we started using clay in the first place. No one is sure why it happens. Small grain size, chemical bonding, and water’s lubricating effect on the stacked crystal sheets all certainly have something to do with it.

There are three basic types of clay minerals, but we’re just going to look at the type of clay that’s usually used in ceramics.
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Georgius Agricola – Renaissance Geologist


"Why, yes I did walk the Earth at the same time as Da Vinci and Copernicus." - G. Agricola

“Why, yes, I was around at the same time as Da Vinci and Copernicus.” – G. Agricola

Georgius Agricola…the name conjures up images of togas, but not at a modern party.

Actually he wasn’t Roman. This German by the name of Georg Bauer just took the Latin name because all cool people did back in the early 16th century. It’s punny: “bauer” means “farmer” in German, and so does “agricola” in Latin (sorry to ruin 24 for you).

But what possible relevance could a Georgius Agricola have today?

Well, he did lay the basis for the mining and metal working industries that have brought you smartphones and skyscrapers. And he could think straight in an age of alchemy and religious fervor.

Agricola didn’t go along with the crowd. While others talked how everything is made of different proportions of earth, wind, fire, and air, he checked things out objectively (and got rich in the process).

And UC Berkeley’s Museum of Paleontology calls him “the founder of geology as a discipline.” So there’s that, too.

Agricola’s life

Unlike some of the earth scientists we’ve looked at, Georg Bauer wasn’t an aristocrat. His father was a cloth merchant in Saxony (part of modern Germany) and was prosperous enough to send Georg to Leipzig University, which was strongly Catholic, in 1517.
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Sayonara, Japan? The Aira Caldera

Update: I have followed this at my other blog with posts on predicting eruptions and on the published paper by the Kobe University volcanologists.

Image of Mount Fuji by Swolib.  Taupo image by NASA

Image of Mount Fuji by Swollib. Taupo image by NASA

Some stark headlines have come out recently, along the lines of “Major Volcanic Eruption Could Make Japan ‘Extinct,’ Study Warns.”

The fuss is over news of a study on Japanese volcanoes that’s due out on November 11.

Kobe University volcanologists Yoshiyuki Tatsumi and Keiko Suzuki-Kamata studied 120,000 years’ worth of eruptions at Aira caldera and other Japanese volcanoes. Some of these have been supereruptions. They discovered that the country faces a 1% risk of such an eruption in the next 100 years.

That doesn’t sound like much, but it’s exactly the same statistical risk that the city of Kobe faced for a major earthquake the day before a M6.9 earthquake happened there in 1995.
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