Obsidian. What does that word mean to you? If it means anything other than a black volcanic rock then you are wrong and should feel bad.
Obsidian is a bit of an oddity in the rock world. Remember that little devil Ozokerite? What a thing that was. Not quite a rock, not quite a mineral, but some sort of slobbering beast stuck between worlds. Well, Obsidian is pretty much in the same boat. If you pretend that Ozokerite is the late President William H. Taft, then it would be fair to consider obsidian as his lesser known brother. Maybe this brother's name is Cornelius, I don't know. I forget the point I was making. Something about how both ozokerite and obsidian are in the same family owing to the fact that they exist in that geological world between worlds. Also I made this.
Obsidian does have a leg up on its less fortunate earthy brother in that there is at least a name for what it is. Obsidian belongs to a class of earth-things known as mineraloids. Which if you ask me is a fancy way of saying "We don't know what you are and your very existence offends us and nature". But fear sometimes leads to poor geology test scores, so let's see if we can't shake out a few of the mysteries surrounding this reclusive mineraloid. Here's what it looks like when you hold a bunch of it in your hand....
(That dog is just asleep on the floor, by the way. No animals were killed during this post). Here is what it looks like when it is piled on top of a rather threatening letter I got from a bank....
And here is what it looks like under a raccoon-skin hat next to a wood carving of two monkeys climbing trees. Let's see another blog give you this sort of variety!
As you can see, obsidian is black. As such, it becomes easy to see how the saying "black as obsidian" came about. Is that a saying? Seems like I've heard that before anyway. But don't get comfy with your "obsidian is always black" frame of mind. Look at this...
Other colors! Plus there's this little devil to deal with....
They call that snowflake obsidian because it melts on your tongue. Nah, it's because those spots look like snowflakes. The snowflakes are just a different form of quartz named cristobalite that is created at the same time as the obsidian. Cristobalite has a wacky atom structure that makes it behave and look completely different than quartz, even though chemically it is all the same crap. Just like William and Cornelius Taft. I'm tired of talking about snowflake obsidian.
So as we can see, obsidian is all over the place. As a mineraloid, it enjoys all sorts of freedomes not afforded to the fully-bonded and insured minerals. Heaven knows you will never find a mineral that shows up in multiple colors.
Anyway, In addition to color, obsidian occupies an unusual range of hardnesses. Look at this part that I've written in bold!
Hardness of obsidian - 5.0 to 5.5!
That's right! A range of hardnesses! While it is true that most mineral specimens will show some small range in hardnesses, it is far more common for a pure mineral to stick pretty close to one number on the ol' hardness scale. But also sometimes not. Who are you to keep pestering me about this? I'm not geology's lawyer! Leave my client alone! A quick review of our handy Moh's Hardness Scale review sheet tells us that a hardness in that range means that sometimes your pocket knife will deal a deathblow to obsidian, and sometimes the other way around. Either way, you shouldn't probably keep both of them in your pocket at the same time. In fact, if you are a the type of person who would do this, then you are likely the type of person who should also read Dr. Seuss' lesser know book "One fish Two fish, both of which are suffering from debilitating groin injuries".
So, why is this so? Why does obsidian refuse to adhere to our tightly knit world of organized....organization? What is it rebelling against? Well the answer has to do with the point I think I was making with the President Taft part. Much like President Taft's shifting political position on many key issues, obsidian doesn't have a set chemical formula!
This means I couldn't tell you what obsidian is even if I wanted to. What I can say is that obsidian usually contains around 70% or more silicon dioxide (that's common glass folks!), with the rest generally being a mixture of iron and magnesium that give it some sort of color as we saw above (again, just like our 27th president)
UNUSUAL FACT FOR FEBRUARY!
Even though obsidian contains (usually) 70% or more of quartz, it has a hardness of 5 to 5.5. BUT QUARTZ HAS A HARDNESS OF 7!!! Behold the mysterious loss of 1.5 Moh Hardness Units! Where did they go?? We may never know! (It has to do with the crystal structure of obsidian! Read on!)
END UNUSUAL FACT FOR FEBRUARY!
In addition to being a veritable funhouse of chemicals, another reason that obsidian is all up in our gills about our ordered lifestyle is that it lacks a crystal structure. What do I mean? For his subject we will have to look into the very heart of the murderous volcano that is responsible for the creation of obsidian. And why stop there? Why not look at the volcano that is responsible for the creation of THIS VERY PIECE???
For that, we must travel to the bowels of Utah. It makes me mad that when most people think of Utah they picture a deserty wasteland populated by polygamists and poor drivers. Sure, you can only see those things, but you will be completely ignoring that we also offer volcanoes and cattle. Now, while it is true that Utah is not the most volcanic state in the union, it certainly has had its share of bubbly explosions in the past, and anywhere you find volcanoes, there is a chance you will also find our mineraloid friend obsidian. The volcano responsible for the piece up above is located in a little place named Topaz Mountain.
Topaz Mountain is a portion of a massive volcanic caldera (bowl). In fact, many of the peaks in the Thomas Mountain Range mark the remains of once mighty magmatic tubes and plugs and whatnot. At some point during the last 42 to 21 million years (Tertiary-aged!) the area around Delta Utah was a lot more exciting than it is now. During that period, this area repeatedly exploded with volcanic ash and deadly volcanic mud and rock breccias. Now days the only explosions around are when the locals shoot cans of Bud Light with various semi-legal firearms. Amazingly, the premise behind both types explosions is pretty similar.
Anyway, yes, if you want obsidian and find yourself in Utah, head ye to Topaz Mountain with all possible haste. The obsidian isn't going to last forever! Only a couple million years. Like everything else, the second obsidian is created it is already doomed.
So why did some of the volcanic emissions end up as glass and other parts end up as those amazing granites we've all heard so much about in our geology magazines? Well sir, the answer is lies with how fast the molten earth-goo cooled. You see, when magma is finally free from the volcano and goes about doing the various things magma does, its molecules are in a state of excitement. They are so excited that they are running around all over the place like me at work.
If you remember back to the days of Jr. High science (should Jr. High be capitalized? Apparently I can't remember my Jr. High english), you will recall that the reason that liquids are so liquidy is because the atoms are moving around all over the place, as the figure above demonstrates. And so it is with lava (and President Taft). Most lava enjoy their time in the sun, then begin to cool and harden. As this cooling happens, the molecules of the various things organize themselves into various crystal forms. I don't know why they do this, but they do. Just blame science. Anyway, for example, here is a quartz crystal...
Now our old pal quartzy here shares much of the same chemical formula as obsidian, but obviously it looks much different. It's likely that the quartz crystal had a long time to cool which in turn allowed the molecules of SiO2 to grow up, go to grad school, get mortgages, and line up to form these crystals. Like so....
That, my friends, is called having a crystal structure. All the cool minerals have them. Well, some of them do. I dunno. Obsidian didn't get that option. for some reason, the happy excited molecules pouring out of the volcano were cooled way faster than those above. Sometimes this happens when lava flows into cool water or perhaps an abandoned ice cream truck. Either way, the result is that the SiO2 molecules didn't get a chance to do anything with themselves.
So, much like myself, obsidian is stuck in a perpetual state of disorganization and serves as an eternal monument to the dangers of using indifference as a lifestyle.
As if that wasn't enough, it is due to this lack of crystal structure that obsidian cannot be invited to the world of proper minerals. And since it is not composed of minerals, it cannot be considered a rock. And so the rise of the mineraloids took place so it could have a home.
YET ANOTHER FASCINATING FACT FOR FEBRUARY
You know those granites we were discussing (mentioned once) above? THEY (usually) HAVE THE SAME (similar) CHEMICAL MAKE-UP AS OBSIDIAN (sometimes)!!! The granite just had a long time to cool so it could form all those neat black and white crystals that remind me of Oreo ice cream (but taste much different). In sort, obsidian is just granite that drank too much as a teenager and now works at the 7-11.
END YET ANOTHER FASCINATING FACT FOR FEBRUARY
Well, we know how obsidian forms, we know why it isn't a mineral, and we know whatever it was I was talking about in the first half of this post. But what is it good for? Something? Nothing? Well, say you are the type of person who likes cutting things. If this is the case, then obsidian is just the (not) mineral for you. Folks have been using obsidian to make blades, arrowheads, shotgun shells (nope!) and various other edge-related tools for ages upon ages. In fact, if you take the time to look about Topaz Mountain, chances are that you will find an arrowhead or two.
I don't know if it is legal to take them though. So if you get caught you've never read this blog and we don't know each other.
Obsidian is so stellar at the whole cutting thing that surgeons today still use it to slice us open and mess about with our gizzards. Obsidian has been shown to keep their edge down to a molecular level, which is pretty good I guess if you are looking for that special edge in your life.
Obsidian is also considered a semi-precious gemstone (gem-mineraloid). It can be cut into all sorts of things, like pigs!
Or skulls! Kids loves skulls!
And say you have the power to give life to things, then you could conceivably make this dog.
So there you go. A whole new mineraloid for you to think about. Also there's that part about President Taft in there, which was pretty good. Anyway, that's my present to you, the world.