What would be the chemical composition of the crust and core of a planet comprised primarily of diamond?

Question

I’m creating a world for a webcomic and I’m running into some difficulties – namely, my own limitations. I’m not a scientist, and I don’t even know how to start asking the questions I want answered. Anyhow, here are the specs for my system;

My planet Liskuel orbits Kereiol, a 2 billion year old quiescent carbon-rich M star with a temperature of 3,100 kelvins and 40% of the sun’s mass. If it flares at all they are tiny. It has four orbiting planets, only one of which, Liskuel, is within the goldilocks zone. Liskuel is 0.15 AU from Kereiol and has an orbital period of 35 days.

Liskuel is a tidally locked wet, rocky carbon-born planet with an active core. The surface is 70% covered by deep water and 30% dry land. It is 1.5 times the size of earth with a surface area of 1147.5 million square km, but with a similar mass and gravity to earth.

This is because, unlike our planet which is dominated by oxygen and silicates, Liskuel is rich in aluminium, titanium, silicon, carbon, and lithium and mostly comprised of quartz or diamond. (For aesthetic reasons, mostly. Webcomic!)

Is this premise possible?

Cheers!

Answer 1

Diamond would form below the crust of your world, so the only surface presence would be from volcanism. A larger world would have more volcanism, but it would still limit the amount found on the surface. There would be more than on Earth, but still fairly uncommon. With the abundance of aluminum, as you said, you would also have an abundance of corundum (ruby) crystals. If there is an abundance of silicates, than you may have more quartz crystal structures found, but I cannot imagine this to be a crystalline world from these.

Now, graphite and graphene can make crystals. If your world was very metal poor and overly abundant carbon, then you may have a landscape with graphite and graphene crystalline structures common on this world.

Answer 2

Of course it's possible!

Obviously, on DeBeers World, some titanic force back in the deeps of time caused all that carbon to be crushed & shaped into a core of pure adamant and a rather gemmy crust. Diamond is formed from carbon essentially through application of high heat and strong pressure, such forces as are found deep in Earth's crust or up in Jupiter's storm clouds. There's thought that Jupiter and other gas giants may even have liquid diamond oceans with solid diamondbergs floating thereon.

This is a fundamental concept in geopoesy, especially of this more scientifantastic sort: You make the world, you set its rules. Don't worry that you're not a scientician --- just take their goodies and run! So I say go for a diamond crusted world!

Answer 3

I'm not sure if this is a very extended comment or an actual answer, but here goes...

Your planet, as you describe it, cannot possibly support life. Of any kind.

Ultimately, a planet that supports life needs two things; a plentiful element of high valency, and an oxidising element. Let's deal with this latter one first.

As the term suggests, the most common oxidiser out there (by far) is oxygen. This is an element that reacts with other elements to release energy out of chemical bonds. In respiration, earth based animals breathe in oxygen, mix it with carbohydrates to produce both water and CO₂. These compounds are in a lower energy state, meaning that the conversion from sugars and molecular oxygen to water and carbon-dioxide has released energy, which the animal uses to live. You can also use other elements, like flourine, but in the vast majority of instances oxygen is going to be the element you use because generally speaking (not a hard and fast rule) the lower the atomic number of your element, the more prevalent it is in the universe.

Either way; without some form of oxidising element, you can't have life.

Now let's deal with valency. We're called carbon based life forms because carbon as an element has a valency of 4. I won't spell out the details of this other than to say that this is a fancy way of saying that you can connect more atoms together with carbon than you need carbon atoms, which in turn means that those hideously complicated organic compounds are now possible. Elements with a valency of 2 (for example) can't support life because there's a limit to the molecular complexity that they can support.

Now, Silicon and (in certain situations) Chromium are also high valency elements, but again carbon is the most prevalent in the universe, and your planet with a high amount of diamond means a high amount of carbon. But, it's locked up in a crystalline form and you really need carbon to be freer in your environment to support life.

So; your planet has to have oxygen and carbon in large amounts to support life. There also has to be other elements, but those are the ones that really count unless you're getting really exotic and creating silicon based flourine breathing life, which might actually work on your planet (but I digress).

Ultimately, there are limits to your planetary design, and I've already written a primer in xenobiology for another question, which might also be useful for you in designing your planet. The important point though is that if you have a carbon based life, you still need oxygen, and the carbon can't be locked up in crystalline lattices that don't wear down releasing freer carbon forms into the environment.