Message 31 of 88 (790340) 08-29-2016 3:31 PM

Reply to: Message 29 by jar 08-29-2016 12:54 PM

Sure, mechanical and chemical processes can obviously both operate on the same lump of rock. Often one will predominate: if, for example, a lump of granite is buried in the humid acidic flood of a rainforest, then that's going to be pretty much all chemical weathering. A cliff face will get pretty much all mechanical weathering and erosion.

Yeah, mica is a sheet silicate, which explains why mica comes in sheets.

I don't know much about asbestos, but wikipedia says that it can be formed from amphibole minerals, where the silicates form a double chain, which would explain its fibrous consistency; or from serpentine, which is a famly of minerals that can take on different crystal habits, but presumably the ones you make asbestos out of have chains or double chains.

Message 32 of 88 (790343) 08-29-2016 3:51 PM

Reply to: Message 24 by jar 08-29-2016 11:56 AM

Irregular means not perfectly flat.

Message 33 of 88 (790348) 08-29-2016 4:01 PM

Reply to: Message 30 by herebedragons 08-29-2016 1:06 PM

Basically, the greater the distance of transport, the finer the grain size and rounding of rock fragments. But then, some materials will break down faster, so be careful.

Sediments will sort in a water medium according to grain size with finer materials being suspended longer (carried farther out to sea) or settling out last in a still column of water.

Message 34 of 88 (790351) 08-29-2016 4:16 PM

Back in Message 6 edge mentioned a second family of processes, chemical sediments that precipitate out of water such as chert, or evaporites, or travertine, or various types of iron formations. I imagine that for things to precipitate out they must first be suspended in water and so once again they must exist before they can be precipitated out.

Is that correct?

What is chert and travertine.

Would limestone and chalk fall in the clastic category?

Are the mineral salts examples of precipitates?

AbE:

edge's reply while I was writing this adds another question.

What is the difference between lithification and metamorphism.

Edited by jar, : see AbE:

Message 35 of 88 (790373) 08-29-2016 6:32 PM

Reply to: Message 34 by jar 08-29-2016 4:16 PM

Travertine is calcium carbonate deposited by hot springs.

Chert is any fine-grained quartz, however deposited; hot springs can deposit it, but there are other ways.

A clast by definition is a bit broken off a rock, so in general no, limestone (of which chalk is a subset) is formed from calcareous parts of organisms and so is a biochemical sedimentary rock.

Of course, you can have rocks made of clasts of limestone, but they had to be produced by mechanical weathering and erosion of limestone, which had to be produced biochemically. Here's some limestone breccia (breccia because the clasts are big and unrounded).

Yes.

Lithification is the process of turning into stone; metamorphosis changes the properties of a stone.

Message 36 of 88 (790374) 08-29-2016 6:46 PM

Reply to: Message 35 by Dr Adequate 08-29-2016 6:32 PM

Thanks. So neither term actually says how hard the stone will be or anything else specific unless the exact materials are also specified?

Message 37 of 88 (790375) 08-29-2016 7:23 PM

Reply to: Message 36 by jar 08-29-2016 6:46 PM

And indeed the exact process. Metamorphosis has different results depending on the degree of temperature and pressure. (For example, I mentioned foliation above: this only happens when there is pressure, heat alone won't do it.) Or in sedimentation, to take a simple example, mudstone is produced by compaction by the weight of the overlying sediment/rock. Nw there is in fact continuum from loose wet mud to the hardest mudstone, and how hard it is will depend on how much it has been compacted.

Message 38 of 88 (790391) 08-30-2016 6:27 AM

Reply to: Message 14 by Percy 08-29-2016 7:56 AM

The valleys at the bottom look very similar to glacial valleys. U-formed. And then the drumlins and striations and all that. Those deposits (the Ecca Group) started being deposited above glacial deposits in U-forming valleys, continuing deposits spilling over into deltas into a relatively shallow body of water. Then we can test for whether the lake was salty or fresh. Rocks forming from salt water have lots of different isotopes than those forming in salt water. Just like we find in deltas today.

Edited by Pressie, : No reason given.

Edited by Pressie, : No reason given.

Message 39 of 88 (790393) 08-30-2016 7:07 AM

Reply to: Message 36 by jar 08-29-2016 6:46 PM

Edited by Pressie, : No reason given.

Message 40 of 88 (790398) 08-30-2016 7:49 AM

Reply to: Message 33 by edge 08-29-2016 4:01 PM

I guess I didn't understand the question. About chemical and mechanical weathering occurring during lithification, since lithification occurs after burial, how could there be any weathering? And about after lithification, can't weathering only occur after exposure?

--Percy

Message 41 of 88 (790448) 08-30-2016 11:50 AM

What are bioherms and how are they identified?

What are other examples of biological material rocks?

Message 42 of 88 (790525) 08-31-2016 9:56 AM

Reply to: Message 37 by Dr Adequate 08-29-2016 7:23 PM

From that I would guess that the deeper something is buried the greater the compaction. Also the longer something is buried the greater the compaction and cementation.

For cementation though I assume what is needed would be water and minerals leached from the overburden. Is that correct?

Message 45 of 88 (790559) 08-31-2016 6:43 PM

Reply to: Message 41 by jar 08-30-2016 11:50 AM

Or coal? (actually, according to strict definition, coal is not a rock).

Or radiolarite? (https://en.wikipedia.org/wiki/Radiolarite)

Or phosphorite? (https://en.wikipedia.org/wiki/Phosphorite)

I'm sure that I'm missing some more ...