Indholdsfortegnelse for September 2025 i Rock and Gem

Obsidian is volcanic glass. Producing razor-sharp edges when knapped, it’s long been used to craft spear points, arrowheads, knives and other practical tools. Coming in varied colors and hues and taking a high-gloss polish, it’s also been used to produce coveted decorative objects. Artifacts crafted from obsidian unearthed in Templo Mayor in Mexico City suggest complex trade networks spread across Mesoamerica during the period of 1375-1520 C.E. As described in Proceedings of the National Academy of Sciences, a team led by Diego Matadamas-Gomora (Tulane University) examined 788 obsidian artifacts unearthed from what was once called Tenochtitlan, the capital of the Mexica (Aztec) Empire around 1430 C.E. Using geochemical compositional analysis, they were able to trace the geological sources of different artifacts and discovered that they came from far and wide.…

The word “sloth” is a major-league pejorative, implying one is slow, lazy, and disinclined to productive activity. To be slothful is one of the Seven Deadly Sins. So pity the poor sloth, today represented by six arboreal species that cling upside down to trees, are nearly helpless on the ground, and move so little that algae and fungi grow within their fur. It wasn’t always so! As detailed in the journal Science, a team of paleontologists led by Alberto Boscaini (University of Buenos Aires, Argentina) took full measure of the sloth family tree over 30 million years of evolutionary history. Far from being a slothful group, they were vibrant, exhibiting exceptional range and diversity. While today’s six species are fairly small, past sloths were large, sometimes quite large; in fact,…

In April, I reported on an article in the journal Science describing a newly discovered 510 million year old critter from the Cambrian Period of China. Guanzxu Zhang (Yunnan University) suggested it was an early ancestor to the mollusks, or a so-called stem mollusk. Time to think again? Now, also in the pages of Science, a new team led by Jie Yang (also of Yunnan University) says: Hold on! It’s really “an early-diverging chancelloriid.” Say what? Basically, a sponge-like animal. These dueling researchers can be excused for arriving at very different conclusions about the same fossils. The period of the Cambrian Explosion saw multicellular life experimenting with all sorts of body forms. The body form of Sishania? Well, it’s been described as “an elongated, bag-like creature covered in spines.” It’s…

Deinosuchus (AKA, Phobosuchus) was a 25- to 40-foot-long gator-like critter prowling both sides of a long seaway that divided North America from the Gulf of Mexico to the Arctic Ocean some 82 to 75 million years ago during the Cretaceous Period. Huge, with fearsome features and teeth as big as bananas, the predator’s scientific name means “terrible (or horror) crocodile.” Given that alligators prowl American swamps today, many considered Deinosuchus an alligator ancestor or relative. No longer. Alligators tend to have a relatively smaller body size and an aversion to saltwater. Instead, they inhabit freshwater swamps. Deinosuchus, on the other hand, was truly immense and seems to have made sojourns across the salty Western Interior Seaway, apparently thanks to saltwater tolerance. Writing in the journal Communications Biology, Jules D. Walter…

"I also found some vugs in the limestone, and these sometimes contained dogtooth calcite crystals. There are also sections of the rock that contain unusual striated features, and I suspect these are aragonite.” Meramec Station Road, located on the outskirts of southwestern St. Louis, Missouri, has a section of limestone cliffs that offer an opportunity to collect calcite. The cliffs are well exposed along the southern side of Meramec Station Road. Parking is adequate for several vehicles, and the area is frequently visited by local rockhounds and people who just want rocks for their garden. The area is best described as commercial and residential. Collecting is along the base of the cliffs, and there are large talus piles along the length of the cliffs. The calcite occurs in small veins…

Millions of miles from Earth, a horde of ancient rocks swirl around the Sun. This spinning band of randomly shaped objects fills the orbital space between Mars and Jupiter, providing us with clues to how our Solar System was created. Known as the Asteroid Belt, this conglomerate of small stellar bodies contains around 1.5 million asteroids, all of varying sizes. Ranging from 327 miles in length to 33 feet, asteroids are made up of a variety of metals. Too small to be considered planets, they do not have enough gravity to hold an atmosphere. Many are as old as the Solar System itself. Believed to be made up of 4.6 billion-year-old primordial material that did not coalesce into planets when the Solar System was forming, the total mass of all…

While relatively few people have ever visited the immense salt flat known as Salar de Uyuni (sa-LAR day ooh-yooni), millions have seen it on the big screen. In the 2017 movie Star Wars: The Last Jedi, Salar de Uyuni was the filming location for the fictional Crait, a small planet where white salt covers bright-red, mineral-rich soil, and the Resistance fought the First Order in a climactic battle. But the notoriety of Salar de Uyuni, located at the lofty elevation of 12,000 feet in remote southwestern Bolivia, goes far beyond its Star Wars connection. Visible from space, it’s the world’s most extensive salt flat, flattest large land area and largest natural mirror. And perhaps most importantly, Salar de Uyuni is also the largest known deposit of lithium. AN ANCIENT LAKE…

While geologists insist Earth is experiencing no more volcanic activity than usual, you wouldn’t know it if examining headlines last June. In addition to prospects of an eruption off the Oregon coast, here are a few other headlines clipped from newspapers worldwide. One of the most active volcanoes in Europe and in the world, Sicily’s Mount Etna has given humans firework displays for half a million years, and it did so again. On June 2, it shot a plume so massive it was captured from space. While not as massive, the Halema’uma’u eruption at Kīlauea shows no sign of abating. Continuing a series of eruptions that have been ongoing for nearly a year, on June 4, it shot a plume 16,500 feet into the sky and lava fountains as high…

Venus is often called Earth’s Evil Twin. While similar in size and position in the solar system, the similarities seem to end there, with Venus proving much more inhospitable. Care for a sulfurous atmosphere and surface temperatures and pressures that can melt lead? But we now know Earth and Venus apparently have another similarity: active plate tectonics, of sorts. Writing in the journal Science Advances, a team led by Gael Gascioli (NASA and University of Maryland Baltimore County) and Anna Gülcher (University of Bern, Switzerland and Cal Tech) report on a large number of active volcanoes they’ve been studying by revisiting 30-year-old images sent to Earth from the Magellan space probe. In particular, they’ve examined so-called coronae, or circular trench-like formations around Venusian volcanoes. It is generally accepted Venus lacks…

It is vital to get accurate readings of the place and time of offshore earthquakes, given their potential for spawning tsunamis and other extreme damage along highly populated coastlines prone to such quakes. Consider the western coast of North America, for example, or all around Japan. When such a quake hits, you want to get a warning out as quickly and precisely as possible. But planting seismometers and other detection devices offshore is much more difficult and problematic than onshore. Now, a research team of seismologists reports how they utilized a ShakeAlert system already in place that they modified by adding historical quake patterns into the standard algorithm used by the system, a modification they call bEPIC. They got their first test of this modification with the December 2024 Cape…

Traditional wisdom holds that material contained within Earth’s core is somewhat fixed and stays deep down. Magma may form in the lower depths of the mantle and ride plumes to the surface to erupt as volcanoes or mid-ocean rifts, but the dense metallic core stays out of it. Well, maybe not. In an article in the journal Nature, Nils Messling (Georg August University of Göttingen, Germany) and colleagues claim to see evidence of “core leakage.” In particular, they’ve found the rare precious metal, ruthenium, in samples of basalt from Hawaii. Hawaii sits above a well-known hot spot, where it’s believed a special concentration of magma rises from deep in the mantle. But this ruthenium evidence suggests that the plume actually originates even deeper, all the way to the core. Ruthenium…

Sri Lanka, formerly known as Ceylon, Ceilão and Sarandib, has been synonymous with colored gemstones for more than 2,000 years. The island nation is famed for its unusually wide variety of gemstones that include spinel, topaz, moonstone, chrysoberyl, garnet, zircon, tourmaline, ruby and, most importantly, the blue and star varieties of sapphire. Sri Lanka’s sapphires are among the largest and most beautiful ever found. Over the centuries, they have earned places in the world’s leading museums and royal crown-jewel collections. Over more than two millennia of mining colored gemstones, Sri Lanka has had its ups and downs. But today, after enduring 443 years of exploitive European colonization, a civil war and a period of technological stagnation that nearly ruined its gem industry, Sri Lanka is again a major player in…

The next time you quaff a cider, thank a volcano. More specifically, thank volcanic basalt formed roughly 10 million years ago in western Colorado, atop what National Geographic Encyclopedia calls the largest flat-topped mountain in the world: Grand Mesa. Rising 6,000 feet above the Gunnison and Colorado River Valleys to an elevation of about 11,000 feet, there are hundreds of lakes to be found along this hard, rugged line of mountains. But… apples? Peaches? And pears? Oh my… At the base of Grand Mesa, at an impressive 6,130-feet elevation of its own, Snow Capped Cider’s orchards in Cedaredge and throughout Delta County have crafted one of the highest-elevation award-winning cideries in the world. At the 2025 GLINTCAP International Cider and Perry Competition, Snow Capped Cider was named Mid-Size Cider Maker…

In January 2025, a group of designers was challenged to create or modify a design for iolite that would show off the gem’s pleochroism and that would work for the material’s lower refractive index and minimal dispersion. Jeffrey Hill’s “Mosaic” is a straightforward design where rough can be oriented to showcase the greys and blues or oriented to show a mixing of the colors. PLEOCHROISM Pleochroism occurs when a gem exhibits different colors depending on its orientation. With iolite, you may see a deep blue/purple and then with a slight shift, that color morphs to a blue/grey, and further rotation will yield a grey/pale yellow color. The reason for the change in visible color has to do with the crystal structure. Iolite has an orthorhombic crystal structure. The same crystal…

The oldest ancestors of four-limbed critters that would lead to reptiles, birds, and mammals keep getting older and older. In particular, I’m talking about amniotes, which evolved to lay eggs on land, not in gelatinous masses in water like amphibians. Until now, the oldest evidence of amniotes came from fossils found in Nova Scotia from the mid-Carboniferous Period, 319 million years ago. Apparently, that’s not old enough. In the journal Nature, John Long (Flinders University, Australia) and colleagues describe a 355-million-year-old sandstone slab from an early Carboniferous formation at Barjarg, Australia, containing footprints of a four-legged critter complete with claw prints at the end of each toe. They say the critter was 2.5 feet long and likely strode proudly erect, not slithering on its belly. The claws tag it to…

A 17-pound rock being used as a doorstop led to America’s first gold rush in North Carolina in 1803. Two centuries later, on another continent, the story replayed with a 7.7-pound doorstop sitting for decades on a Romanian woman’s porch. Upon her passing, folks finally took a close look and found it to be a rare red form of amber. According to an article by science journalist Michelle Starr in the journal Nature, this particular variety of amber is found only in Romania and is referred to as rumanite. Without the precise locality of its origin, its exact age is unknown, but such Romanian amber has been dated at between 70 and 38.5 million years old. It’s believed the stone was found in a stream in the village of Colti…

Many birds migrate to Arctic nesting grounds while others settle in year-round. As many as 280 species either visit or claim the Arctic as home. They do so in part because 24 hours of sunlight during summer months results in great trophic richness, providing abundant seasonal food supplies. This has apparently been the case going back as far as 73 million years. Writing in the journal Science, a group of U.S. and Canadian paleontologists led by Lauren N. Wilson (University of Alaska, Fairbanks & Princeton University) report on fossil birds they’ve discovered from Late Cretaceous Period sediments in northern Alaska. The finds include bones of varied species as represented by both adults and hatchlings. All are preserved in remarkable detail. The new find helps fill in what is an otherwise…

It certainly made for splashy headlines. Nikku Madhusudhan (University of Cambridge) and colleagues announced in The Astrophysical Journal Letters that they detected chemical signatures similar to those produced by phytoplankton on Earth, which release dimethyl sulfide and dimethyl disulfide into the atmosphere. Both signatures may have been detected within the atmosphere of an exoplanet called K2-18b, a planet some 700 trillion miles away. They called it “the strongest evidence yet there is possibly life out there.” They made their observations courtesy of NASA’s James Webb Space Telescope. The news took the press by storm, even though Madhusudham’s team cautioned the need for more data and offered alternative explanations. That caution proved justified, for no sooner did they report their findings than skepticism flowed in. Some claimed geological activity, not life,…

Many minerals exhibit fascinating special effects that are no less than magical. You’ve likely heard of some, like magnetism or fluorescence. Minerals exhibiting such properties are fun not just to collect, but also to play with and share. To illustrate special effects, I’ve pulled together demonstrations I’ve dubbed “The Amazing Mineral Magic Show.” Here’s how you, too, can provide fun for rock club kids, gem show visitors, students during classroom visits, or kids, parents, and teachers in an attention-grabbing Science Night booth. MAGNETISM: FEEL THE PULL! We’ve all had fun with magnets. Place them near a steel surface, and they literally jump from your hand. They attract and repel other magnets, letting you flip one around with another without them touching. Magnets perform such stunts because they produce a field…

Sunstone is the transparent, gem-quality variety of the mineral labradorite, a calcium-rich feldspar in the plagioclase series. It is one of the most popular U.S. gems and is notable for its warm colors and internal shiller (shimmer). Its specific shimmering effect is called aventurescence, uniquely caused by tiny copper platelets within the crystal. Unlike most feldspars, which are opaque or iridescent, Oregon sunstone is prized for its transparency, with the best Oregon sunstone gems having the most brilliant shimmer and saturation. Formation Oregon sunstone formed in volcanic environments, specifically within the cavities and flows of basalt. Copper gets trapped in sunstones as they form from cooling lava rich in copper. As the crystal grows, tiny flecks of copper become locked inside, creating a sparkling, metallic shimmer. This natural shiller is…

Every year comes the chance to find something new, whether in the field or the marketplace. This year, a new type of jasper appeared in the rockhound community on Facebook, catching quick attention for its bright variety of colored poppy jasper. Duncan poppy jasper is found along the Arizona/New Mexico border and is a brand-new find by journeyman Tim George. On one of his adventures hiking across old volcanoes, he discovered a small deposit of this cranberry-colored poppy jasper. In his recollection, he realized he missed the first deposit by 50 feet. This bright new material contains various colored poppies, prominently deep reds and oranges, with one variety being pastel purple and pink flowers too. Often, you will find many quartz crystal pockets and agate veins running through, making for…