11 votes
Accepted

Why there are no sharp corners in nature?

The premise of your question is entirely wrong. There are many examples of sharp corners in nature, the most obvious being well formed crystals. Pyrite is a classic example that was mentioned by @...
bon's user avatar
  • 2,211
8 votes
Accepted

What is this fossil? What is this crystal?

Yes, this is a rather nice find; an ammonite of the Jurassic in central Europe. Given the size of the specimen, and its appearance, this appears to be of the species Cardioceras, or Perisphinctes. ...
Thomas Perry's user avatar
7 votes

How can the 'crystal cleavage' of apatite have a four-digit number?

This is not a four- digit number but four separare numbers called Bravais-Miller indices. Bravais-Miller indices descrive the orientation of a crystal plane relative to the symmetry axes of a crystal,...
Oscar Lanzi's user avatar
  • 3,831
5 votes

Why does halite have perfect cleavage at the (110) plane?

I think the commenters have identified the issue. Halite does not have perfect cleavage along the {110} plane. As recorded in Mindat, Halite has perfect cleavage alone {100}, {010}, and {001}. This ...
Microscone's user avatar
5 votes

Does Xenon really covalently bond to oxygen within quartz?

Not sure this is appropriate for Earth Science SE (Chemistry SE would be a better fit), but the answer is "maybe". quoting from the same Wikipedia article: Three oxides of xenon are known: ...
Oscar Lanzi's user avatar
4 votes
Accepted

What's the difference between cleavage and fracture?

They are not synonymous. Cleavage means breaking along planes defined by crystallographic directions. For example, cubic crystals like halite, NaCl, often cleave along directions that follow the ...
haresfur's user avatar
  • 4,419
4 votes

When diamonds "migrate" from deep underground to the surface, do they maintain pressure inside when there is no more pressure outside? If so, how?

The question is in regard to pressure confining a rare, deep-mantle formed mineral visible within a diamond inclusion. The pressure on the inclusion within the diamond crystal is really the pressure ...
Thomas Perry's user avatar
3 votes
Accepted

When diamonds "migrate" from deep underground to the surface, do they maintain pressure inside when there is no more pressure outside? If so, how?

One of the more interesting examples of diamond maintaining high pressure in its lattice is discussed in this answer from Space Exploration SE. Put briefly, Ice VII inclusions have been found in ...
Oscar Lanzi's user avatar
  • 3,831
3 votes
Accepted

What does the unit cell of petitjeanite look like?

Should one assume that the mineral petitjeanite and the chemical discussed in the recent Chemical & Engineering News article Photocatalyst shreds drinking water contaminant PFOA are probably the ...
A.K.'s user avatar
  • 146
3 votes

An oblique-square-prism crystal?

If "oblique square prism" is this, where the top and bottom planes are parallel, then yes, there are. Carbonates (members of the Calcite and Dolomite, but not Aragonite, groups) have perfect cleavages ...
Matheus's user avatar
  • 348
3 votes

A few questions about glass

Q1: A volcano consists of many lava flows that occur over a long period of time. In general, only very few of these lava flows have the right composition and the right cooling history that are ...
knb's user avatar
  • 161
2 votes

A few questions about glass

In particular, in season 7 of Game of Thrones, the island of Dragonstone is revealed to contain a veritable mountain of obsidian - is such a thing possible in the real world? I would have thought that,...
Knob Scratcher's user avatar
2 votes

Is there any covalent crystals that can be easily synthesized?

Silicon carbide is covalent and can be synthesized at atmospheric pressure by the Acheson process. Temperatures may actually be somewhat higher than your range but are easily achieved by the process. ...
haresfur's user avatar
  • 4,419
2 votes

is this a rose quartz

Yes, it is rose quartz. There are a number of mines in eastern New York near Vermont where rose quartz been found. Massive rose quartz can occur in granitic pegmatites. I could not google to find ...
Earth Science Expatriate's user avatar
2 votes

Can the formation of gypsum evaporites (sand roses) be simulated in the lab?

Yes, it has. Cody & Cody (1998), Journal of Sedimentary Research. http://archives.datapages.com/data/sepm/journals/v55-58/data/058/058002/0247.htm Abstract: Gypsum crystals were grown in ...
Gimelist's user avatar
  • 23.1k
2 votes

Sources or strategies for stone identification

Are your stones raw or are they cut & polished as they would appear if mounted in jewellery pieces? There are tests such as streak & hardness which can be done to raw stones but not to ...
Fred's user avatar
  • 24.7k
1 vote

Sources or strategies for stone identification

Is there such a reliable source so I can identify the stones by myself? Maybe. Most semi-precious stones are various forms of quartz or silica (e.g., agate, citrine, etc). Quartz is very hard and ...
Gimelist's user avatar
  • 23.1k
1 vote

Geode-like rock but it's empty inside. Why does this happen?

Geodes form where there is a gas bubble or some other sort of cavity in volcanic or sedimentary rocks. I once found scores of them eroding out of a sea cliff in Oman, and they looked very similar to ...
Michael Walsby's user avatar
1 vote

What does the unit cell of petitjeanite look like?

Having the same formula does not mean that the crystal structure is the same. An example is calcium carbonate, which can form the minerals calcite or aragonite. So you have to read the publications to ...
haresfur's user avatar
  • 4,419
1 vote

What type of yellow-green stone is this?

I think your mineral specimen is smithsonite based on texture and the dark metallic specks that appear to be galena.
Earth Science Expatriate's user avatar
1 vote

What determines a mineral's hardness?

the strength of bonds that hold the meniral the structure of the mineral lattice crystal morphology
Yasmin mabed's user avatar

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