10
votes
Are there minerals which are not been found on earth but which are still possible to exist?
To answer the first part, there are many minerals on earth which do not involve silicate bonded structures. For instance, non-silicates (minerals of carbonates, sulfides, sulfates, phosphates, and ...
- 101
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
6
votes
What is the white coating "patina" we often see on deposited chalcedony/agate?
The white "patina" is most likely some form of opal as you suggest. I did some research and I'll explain how the agate becomes opal and why it's more common in the eroded rock.
Some ...
- 354
5
votes
Is every space group realized by some mineral?
Now all of the 230 space groups are realized by a natural occurring mineral.
I found this blog: crystalsymmetry.wordpress.com where space groups are listed with at least one chemical compound is ...
- 5,959
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
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
4
votes
Accepted
To find hardness in Mohrs scale
Although this is a somewhat poorly researched question, I think there is an opportunity to make a nice point here.
First of all, let's look at the Mohs scale:
Talc
Gypsum
Calcite
Fluorite
(fluor)...
- 23.3k
4
votes
How can a crystal habit be round?
Botryoidal habit describes the arrangement of a large group of hematite crystals.
While hematite's trigonal crystal system describes the geometry of a single unit crystal of hematite, the two ...
- 5,959
4
votes
Are there minerals which are not been found on earth but which are still possible to exist?
We might also consider minerals that cannot appear as minerals on Earth because Earth is too hot. These would be ices that exist in solid form, and meet the standard definition of minerals, mostly ...
- 4,041
4
votes
Are there minerals which are not been found on earth but which are still possible to exist?
First of all, there is this question and answer that might be relevant:
Were all of Earth's minerals created before Earth's formation, during, or after?
Also notice the bit about "mineral ...
- 23.3k
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
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
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
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
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
Why do snowflakes form into hexagonal structures?
The question asked is "why do snowflakes form into hexagonal structures".
I see snowflakes as following the framework of a flattened cuboctahedron.
- 437
3
votes
Are there minerals which are not been found on earth but which are still possible to exist?
To put things in perspective, as Tachylite says, there are about 5150 known natural mineral species on Earth. Despite more mineralogists and better analytical equipment than ever before, the discovery ...
- 14.3k
3
votes
Accepted
What exactly are enantiotropic and monotropic polymorphic transitions?
If you can get your hands on a copy of Fegley's book Practical Chemical Thermodynamics for Geoscientists, he gives a good description in Chapter 07, which I'll summarize here.
An enantiotrope is a ...
- 380
3
votes
Simple explanation of what "preferential lattice expansion due to excessive magnesium adsorption", means
Dolomite is a form of calcite in which magnesium replaces some percentage of the calcium in what is otherwise a calcium carbonate rock. Magnesium has the same charge, and thus bonding behaviours, as ...
- 5,165
2
votes
Accepted
Iron-nickel phase in pallasite meteorites
First, a correction. A solid solution is between different compositions in the same phase. For example, olivine is a solid solution of forsterite (Mg2SiO4) and fayalite (Fe2SiO4).
There are two common ...
- 23.3k
2
votes
Accepted
Difference between crystal and mineral
A crystal,
is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions.
...
- 25.1k
2
votes
What is a good definition for "lattice bound" and is iron within octahedral sites of illite considered lattice bound or interstitial?
We definitely have +2 and +3 ions bonded within the same type of site. And it's not just iron; magnesium can become involved among the +2 ions and aluminum among the +3 ions. As for whether they are &...
- 4,041
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 exactly are enantiotropic and monotropic polymorphic transitions?
A solid to solid transition can occur between two enantiotropically related polymorphs without going through a melt. Whereas for monotropes conversion can only take place once the material has melted. ...
1
vote
What is the white coating "patina" we often see on deposited chalcedony/agate?
It is chemical weathering. It is caused by reaction to sunlight or caustic pH in soil that starts breaking down the non silica impurities in the agate. Heat from a natural forest fire can also cause ...
- 11
1
vote
What is the white coating "patina" we often see on deposited chalcedony/agate?
In Arizona, I find this coating on agates/chalcedony. But, I think it forms in a reaction caused by the sun, as it will be on the top of the rocks and not on the underside in contact with the soil.
1
vote
How can crystal habit be determined when rock is worn and rounded?
Is there a simple instrument
A geological hammer. Seriously. Once you smash a rock, you reveal fresh cleavage planes, grain boundaries, less weathered zones, etc. The downside is that it's ...
- 23.3k
1
vote
Is every space group realized by some mineral?
Quoting a mineralogist friend of mine:
I think there are mineral representatives of all 230 known by now - some of the groups are much rarer than others, but there is nothing specifically ...
- 23.3k
1
vote
Are there minerals which are not been found on earth but which are still possible to exist?
There are a vast number of hypothetical minerals that will not form or persist in the presence of water, particularly liquid water. Since the Earth's mantel and crust are sodden compared to Mercury, ...
- 571
Only top scored, non community-wiki answers of a minimum length are eligible