World-Building #7

Some Basic Minerology for World-Building

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A century of spectrographic analysis of distant stars has shown that the building blocks of the elements are pretty evenly distributed throughout the universe. You are not going to run into a section of galaxy where there are human-habitable planets with no trans-uranic elements, or no sodium, or no carbon.

Note the term human-habitable planets. That's where the action almost always takes place, right? So discussing what's present in stellar cores is by the by. If you want something exotic, you are going to have to sit down to the study of astrophysics. If you want to see how that works, check the introductory material to H. Beam Piper's Uller Uprising, where the astronomy, chemistry, and life forms are worked out for a silicon planet and a fluorine-based one. The essay was done by Dr. John D. Clark around 1951, and is a brilliant example of what you need to know about an exotic planet.

Planets seem to form in three types. What's under the methane on gas giants is only subject for debate. Considering that these are virtually still-born stars (Jupiter classes as a dark companion to Sol), it might be rather bizarre. Whatever it is, is heavy from accumulated mass, even if its average density is low. Odds are, there is no "planet" at the center: there's just a steady spectrum from gas through fluid to solid, without crust.

At the other end are the light silicaceous planets, like Luna. Luna isn't really "a moon" by the modern definition of a moon: Terra and Luna are a binary planet. Silicaceous planets tend to be smallish and emphasize the lighter rock forms, indicating a relative lack of heavy elements. This makes them lesser in mass, lesser in gravity, and unable to hold atmosphere worth spit. Jack Vance, wanting a truly vast canvas with Terran gravity, postulated an extremely large silicaceous planet for Big Planet and Showboat World. The size counteracted the lightness of the materials to give him sufficient gravity. These would be freaks, and rare. He played it to the hilt, and made almost all metals "precious metals" -- present only in much smaller quantities than we are used to.

In between are the ferric-core planets like Earth. Almost all self-supportable Terran colonies will be on ferric-core planets, because only these have enough mass to have comfortable gravity and atmosphere, without tilting into excess mass. As "ferric" clued you, these worlds have plenty of metals like iron.

It is postulated that the crust of ferric planets can eventually be mined out by sufficiently industrious inhabitants. A. E. Van Vogt used this as one of the aspects of a truly ancient Earth in The Book of Ptath. Others like Clark Ashton Smith in his Zothique stories, or Vance in The Dying Earth have not carried industry or lack of crustal renewal so far. This mining would only affect the relatively thin skin accessible to humans; the mass of the planet is in the hot core, and would not be changed. So, no, millennia of mining will not change a ferric planet to the weight of a silicaceous one, or change the mass to notice on a planetary scale.

A Rock is a Rock, Unless It's an Icecube

The processes of geology are merely the planetary extension of those of astrophysics. They are universal, and not unique to Earth. Lava, under the various conditions of pressure, exposure to air or not, original chemical mix, etc., cools to form certain kinds of rocks (igneous), breaks down and reforms into others (sedimentary), and is rebuilt by underground pressure into a third class, metamorphic rocks.

An example is quartz, an igneous rock, which weathers into grains. These sand grains gather as sediments into sandstone. I've dug for fossils through semi-consolidated sandstone, halfway between sand and stone, so the part-way points are around, too. When sandstone is compressed by huge layers of other rocks above it, it metamorphs into shale.

The names used are not "local" ones for things that only exist in one place. Every rock brought back by NASA or incoming meteorites has fallen into one of the three known mineral type; none of them have ever been "unearthly minerals" never before seen.

By definition, a mineral is a naturally-occuring solid crystalline structure of matter. Sand is a mineral. Clay is a mineral. Native silver is a mineral. Rock salt is a mineral. Ice is a mineral. No one said the mineral had to be enduring.

Petroleum is not a mineral: it's liquid and does not have a crystalline structure. Elements only produced in labs can't be called minerals, because they can't be proved to exist normally on planets. "Soil" isn't a mineral, because it is a complex blend of minerals and organic humus, which isn't crystalline. If swamp dragons poop crystals, though, they would be a mineral, because they occur by nature. Most geologists, though, would then want the extension "occuring naturally by geologic processes." They should have thought ahead. Yet oolitic limestone is pressed from massive desposits of organic shells, and it's a mineral. Amber is really ancient resin, aged more or less hard, and it's a mineral.

Minerologists identify a rock by looking at it, checking its texture, its hardness (resistance to scratching, not resistance to blows, which is toughness), its color, its kind of fracture and lustre. Sometimes you even taste the things -- cautiously! -- because that's the fast way to ID rock salt, and a few others. If all the characteristics match a certain already established type, then by jingo that's what this rock is, too. The fact that it is found on a different continent or planet is utterly immaterial.

Some minerals are more common than others. Ferric-core planets are built largely of basalt and granite. Silicaceous minerals like sandstone, quartz, and shale are extremely common. So are any mineral forms based on very common elements.

In world-building, it would be safe to assume that any fairly common mineral with more than one source on this planet is likely to be universal and known on Earth, especially when it has been known since the dawn of time. Shale, marble, limestone, ochre, obsidian, basalt, gabbro, granite, slate, sandstone, gneiss, travertine, and other well-known building stones can be assumed. So can semi-precious minerals and precious stones like turquoise, carnelian, jasper, agate, quartz, chalcedony, lapis lazuli, jadeite and nephrite (both of which are considered gemstone jade; the idea that only jadeite is "true jade" is ignorant of history and gemology; the minerologic division is very modern, and the names could easily have been swapped when set up), malachite, spinel, corundum (rubies and sapphires), opals, and even diamonds. Diamonds are a form of the extremely common element carbon; most are industrial rocks, and only a small percentage gem-quality. It's the gem-quality ones that are rare. They are associated with old volcanic pipes and blue clay dikes all over the planet.

On the other hand, minerals so rare they were only discovered and named in the 20th century, or occuring in only one location may be considered to require such special conditions that they may not have happened on your planet. Examples might include dichroic alexandrite, tanzanite, or andesite. Your planet may have as rare items its own minerals. However, be careful that when you invent a new mineral that you give it a new name. Just as you would not call a new animal an okapi or quagga because it would confuse the reader who already has a mental image for okapi or quagga, you need to check the dictionary in case there is already a sunstone, silverstone, bloodstone, peacock stone, electrum, sealstone, kunzite, etc. (All of these are already taken.) There are hundreds, thousands of mineral names that non-minerologists have not heard of, or heard of once only to have them surface as a "new name" thanks to cryptomnesia. If it's dramatic and descriptive, odds are it's taken, so check! Lots of others based on people's names are, too.

If you can't use bloodstone, though (it's a birthstone for Aries, a green jasper with red spots or red with green spots, depending on how you cut it), you can hit the thesaurus and look for a new variation. Gorestone? Not used, and actually more atmospheric. Sanguinite even sounds mineralogic (formal names for minerals all end in "-ite"; those for elements end in " ium"). But why invent a new mineral? If it needs peculiar properties for the story, okay. Otherwise, if it is strictly atmospheric, an extant mineral will do the job and be a more vivid image for those familiar with it. "If all the characteristics match a certain already established type" you might as well not name rabbits smeerps.

Magic Minerals

All right. Sometimes you do need a new mineral to be used in technology. As in, we didn't get good FTL travel before we had this stuff, found by one of the robot starships. Maybe it's the only cure for space flu. Maybe it makes magic work.

You can invoke the idea that this is one of those special minerals like dichroic alexandrite. In fact, all those 20th century specials have been variations on a known mineral, so they haven't revolutionized technology.

This is where knowing the three types of rocks can bail you out. There are not likely to be any igneous, first-stage rocks that are bizarre. However, once they physically or chemically break down into particles, they can be recombined by water into all sorts of sedimentary rocks.

Some sedimentary rocks are partially or entirely organic in source (one reason to ignore the geologist who has to eliminate swamp dragon eliminations from minerals). Sedimentary rocks are often dated by the microscopic shells and pollens in them. In the petroleum industry, people who prepare samples for dating and do the dating, glory in the titles of "bug washer" and "bug picker," the "bugs" being diatoms and other micro-shell critters who build shells of silicon or lime and left them behind in the sand. Sometimes they are so thick there is almost no sand among them. There are fossilized coral reefs, as well. Other organic minerals are coal and amber. Coal is peat aged and compressed until it forms crystalline structures.

Now, let us say that in ages past some micro-beastie made its shell out of something strange, or built the normal stuff into bizarre structures, so that the fossilized shells have odd properties. You could have something like a coral reef built along streambeds that in floods get buried and started on fossilization. You could have your organic start in nests built above or below ground, like the iron-hard termite nests of Africa. When they become part of the geology, they may have the strange characteristics you need without either getting you into quantum physics or your more scientific readers into a swivet. We always allow that biology is lots stranger than chemistry or geology: biology is allowed to be an alchemist.

If, on top of that, you only get your mineral when the sedimentary rock undergoes heating and/or compression into a metamorphic form of the rock, you can make it pretty rare even on one planet, even though when found it will be in large masses.


Recommended Reading: Though I'm normally kind of down on Time-Life Books, their Planet Earth series was an excellent introduction to the various aspects of geology and climatology. It's accessible to the beginner, but interesting to the more advanced, beautifully illustrated, and clearly written. They slipped!

Otherwise, it certainly won't hurt to stop in at the local college and buy a second-hand copy of the Geology 101 textbook. Make sure it has chapters on minerology, not just landforms and plate techtonics.


Authoritative Background: As a kid, the variety in rocks fascinated me and my attempt to collect piles of them did not please Mom. In my first college career, my minor was geology, and my geology prof kept trying to get me to major in it. I've been in the field, and made the crucial professional choice between landing on one knee on a cactus or dropping the fossil. Flesh heals: broken fossils don't. Since then, I've maintained an active interest in the field, and expanded my minerology lab background into gemology. That resulted in a lead article in 'Dragon Magazine' in 1998 on gemology. I took a semester of astronomy, having enjoyed the astronomy section of high school physics, and my husband got so far into astronomy that he ground and silvered mirrors for his own hand-built telescopes. We have interesting discussions of the seasons of Uranus and the latest evidence for the commoness of planets in stellar systems.

 

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Some Basic Minerology for Planet Building