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. ...
- 96
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,...
- 4,041
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 ...
- 151
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: ...
- 51
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 ...
- 4,427
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 ...
- 41
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 ...
- 4,041
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 ...
- 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 ...
- 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 ...
- 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,...
- 2,813
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 ...
- 5,959
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 ...
- 23.3k
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 ...
- 25.1k
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 ...
- 23.3k
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 ...
- 4,711
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 ...
- 4,427
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.
- 5,959
1
vote
What determines a mineral's hardness?
the strength of bonds that hold the meniral
the structure of the mineral lattice
crystal morphology
- 11
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