Some Basic Minerology for World-Building
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,
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
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
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.
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
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
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.
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.