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[Yag Alone]

Hello there

I had a strange idea today : trying to made a diamond mine... after some quick examination of the raws (let's just say it's "common dwarven knowledge"), I discovered that diamonds appears as small clusters in kimberlite :

code:

[MATGLOSS_STONE :DIAMOND_FY]
[TILE:15][GEM:faint yellow diamond:STP][COLOR:6:7:0][VALUE:40]
[SPEC_HEAT:409]
[IGNITE_POINT:11440]
[MELTING_POINT:NONE]
[BOILING_POINT:16708]
[ENVIRONMENT_SPEC:KIMBERLITE:CLUSTER_SMALL:100]
[SOLID_DENSITY:3520]

Right, time to look for Kimberlite.... but where should I look for it?
Raws still have the answers : gabbro!

code:

[MATGLOSS_STONE:KIMBERLITE]
[NAME:kimberlite][COLOR:1:7:0][TILE:'%']
[ENVIRONMENT_SPEC:GABBRO:VEIN:100]  

Gabbro is one of the basic kind of layer rock, so let's just head to a place with several of those layers... and...
I tried a couple of full sized region wide fortress on area with large gabbro layers, reveal confirmed the presence of gabbro, Olivine and its tasty chromium veins, as well as garnierite, both gabbro specific, are very common...
But not a single rock of Kimberlite can be found.

Perhaps I was very unlucky, but I wonder if anyone of you ever found this kimberlite?

(btw, same question for some other weird useless ores, for example Realgar or Orpiment - I never found any of those on my volcanic fortresses)

[Salmeuk]

This is a good question, as I have also started many fortresses in gabbro, but only ended up with olivine. I have no idea why this might be, though.

[RPB]

I've noticed a lot of rock types having a far more limited selection of minerals than is suggested in the raws. Not sure what's up with that.

[Durnheist]

In my search for the ideal location for a fort I have looked at many many layers of gabbro.  I have never seen kimberlite in all that time, and I've looked specifically for it a few times just to see.  I have also never seen rock crystal yet, which is supposedly common, and occurs in all rock types.

[Zurai]

I have seen rock crystal, but never kimberlite or diamonds. I havn't seen the dwarves offering to bring diamonds, either.

[Sean Mirrsen]

I've also seen a single pocket of rock crystals, but it was on the bottommost layer of rock of my latest fort, and found only after much cross-prospecting. There's some gabbro too, so I'll see if I can find some...

Edit: wait, wait...  I see "SPEC_HEAT" in that raw definition. Doesn't that mean that the diamonds will only occur in heated areas? As in, near magma? Sorry if the comment's stupid, but I just want to make sure.

[ November 15, 2007: Message edited by: Sean Mirrsen ]
Edit2: No, the comment's not stupid. Only diamonds have that tag. That means that the target area for diamonds is a kimberlite vein in a volcanically active area, and deep underground where it's warmer.

On another note, I found black opals in that fort, that have 8% chance of occuring, even though in all kinds of stone...  I should get lucky with diamonds, right? Especially since I specifically chose that location in hopes of finding magma...

[ November 15, 2007: Message edited by: Sean Mirrsen ]

[Haedrian]

What I lyke about this game is that its so realistic.. you can wiki stuff  

quote:The formation of natural diamond requires very specific conditions. Diamond formation requires exposure of carbon-bearing materials to high pressure, ranging approximately between 45 and 60 kilobars,[12] but at a comparatively low temperature range between approximately 1652–2372 °F (900–1300 °C).[12] These conditions are known to be met in two places on Earth; in the lithospheric mantle below relatively stable continental plates, and at the site of a meteorite strike.

Okaaaay, what does that translate to in game terms?

[Sean Mirrsen]

Like I said, a gabbro layer with a kimberlite vein next to an underground magma river, or possibly demon pit. If you encounter raw adamantine, the conditions there are pretty close to what diamonds need.

[Arkose]

If it helps, I can explain why diamonds are typically only found in kimberlite pipes in the real world:

---

Aside from a meteor impact (which will only form microscopic diamonds), the only place with the right combination of temperature and pressure needed to form diamonds is near the contact between the mantle and the thick crust of a continental plate.

Diamonds can't arrive at the surface by being carried up as a xenolith in magma, because the combination of high temperatures and rapidly decreasing pressure will destroy them relatively quickly.

Instead, diamonds encrusting the bottom of a cooling continental plate are occasionally brought up from depth (along with an wide asortment of other rocks) relatively quickly (for a geologic event) to form pipes of kimberlite. I don't think it is known for certain why these erruptions of rock occur, although there are a variety of theories.

In any case, kimberlite pipes are rather rare, and typically very hard to locate. To make matters worse, almost all kimberlite pipes contain no diamonds whatsoever, and even the very diamond rich ones contain diamonds in an incredibly small ratio to the rest of the kimberlite rock's mass.

Diamonds have also been found occasionally on river banks and the like; they likely come from eroded kimberlite pipes. The number of diamonds found in this manner is incredibly small when compared to the amount mined, however.

---

So basically, it isn't at all unreasonable that you haven't found any diamonds, from a realism point of view. I don't know enough about what the raw's frequency data means in terms of how much gets placed to say if the game is working as intended or not, however.

I don't see any reference to it in the raw data, but I might as well throw this out there anyways: kimberlite pipes that reach the surface tend to weather faster than the surrounding rock, producing rounded pits inside which ponds frequently form; a good number of kimberlite pipes have been found by looking for unusually rounded ponds.

I don't think Toady went so far as to model that feature of kimberlite pipes, though. (At least not yet.)

[Arkose]

quote:Originally posted by Sean Mirrsen:
<STRONG>
Edit2: No, the comment's not stupid. Only diamonds have that tag. That means that the target area for diamonds is a kimberlite vein in a volcanically active area, and deep underground where it's warmer.
[ November 15, 2007: Message edited by: Sean Mirrsen ]</STRONG>

I would imagine that [SPEC_HEAT] is the material's Specific Heat, that is, how much heat energy is needed to raise the diamond's temperature by a certain amount of degrees; I don't think that the data says anything other than that it forms in small clusters in kimberlite veins...

[Stormcaller]

Found rock crystals in a bloodline game, while digging through red sand near the surface. I couldn't tell you conditions offhand as I'm not sure what the seed number or biome information was with regards to the fortress location. All I'm aware of is that I was 1 z-level down on an elevated area, and digging towards a brook when I ran across four rock crystals. There may have been more but I didn't check.