Rocks & Minerals B/C

[kate!]

I don't know if this question was asked before but what are some common minerals/rocks I might be asked to identify in regionals? Like, are some mineral groups/rocks more likely to be tested on than others on the list? Im in division C btw

I'm in div B, but it seems like, based on my experience, there will not usually be gold, silver, or diamond. Also, the three types of coal are common, as are obsidian, calcite, and halite. Most of the ones that look like other rocks/minerals are common, like graphite and magnetite. At my last competition, there were quite a few rocks that contained common minerals, like pegmatite and a schist sample containing staurolite. You should still prepare for everything on the list, though, because it really depends on the event coordinator for what samples are used.

[dxu46]

I don't know if this question was asked before but what are some common minerals/rocks I might be asked to identify in regionals? Like, are some mineral groups/rocks more likely to be tested on than others on the list? Im in division C btw

In my 2 years of experience, I've noticed that minerals with special properties are frequently tested. For example, I've almost always seen a calcite/aragonite station, and a coal carbon content comparison station, etc, because general knowledge questions like streak, density, etc. are going to be free throws for any team with a binder. For this reason I recommend many "fun facts" or random bits of information that you never knew. Like who knew Amethyst was thought to have warded off drunkenness? Or that if you wash Galena with soap and water you will remove any tarnish? Little tidbits like that (in my experience) will help you win.

[whythelongface]

Like who knew Amethyst was thought to have warded off drunkenness?

I actually hate stuff like this, because it's one step away from this to crystal healing and the spirit realm. I am of the opinion that random trivia is the trademark of bad tests - the focus of any given station should be scientific.

But unfortunately, not every Rocks test ends up like Yale or Princeton, so you will have to know the stupid tidbits.

[jpeistrup]

It's a bit of a weirdly specific question, but different websites keep on giving me different crystal systems for Kaolinite. Some say triclinic, some say monoclinic. Which is correct? Thanks so much to anyone who can tell me the answer!

Wow, your right, but most sites seem to say it is triclinic. Triclinic and monoclinic are similar so I see why.

If you have a field guide refer to that to see what it says, a lot of times its more reliable/reputable than websites. I personally am going to go with triclinic as this is what my personal specimen exhibits.

I have a kind of similar question, my field guide has 6 types of crystal habits: cubic, monoclinic, triclinic, trigonal, orthorhombic and tetragonal, but on different websites, they list crystal habits like nodular, octahedral, and prismatic and I'm very confused about the difference between these??

Does anybody understand this? Thanks!!

[kate!]

I have a kind of similar question, my field guide has 6 types of crystal habits: cubic, monoclinic, triclinic, trigonal, orthorhombic and tetragonal, but on different websites, they list crystal habits like nodular, octahedral, and prismatic and I'm very confused about the difference between these??

Does anybody understand this? Thanks!!

The 6 types of crystal habits listed in your field guide are crystal systems (both terms can be used, but it's generally better to use crystal system so you don't mix it up with mineral habit.) Crystal system is the structure of the mineral to a molecular level. On those websites, you may be seeing mineral habits. Mineral habit is the general physical outward appearance of the mineral. Nodular, octahedral, and prismatic are all examples of mineral habit.

[whythelongface]

I have a kind of similar question, my field guide has 6 types of crystal habits: cubic, monoclinic, triclinic, trigonal, orthorhombic and tetragonal, but on different websites, they list crystal habits like nodular, octahedral, and prismatic and I'm very confused about the difference between these??

Does anybody understand this? Thanks!!

The 6 types of crystal habits listed in your field guide are crystal systems (both terms can be used, but it's generally better to use crystal system so you don't mix it up with mineral habit.) Crystal system is the structure of the mineral to a molecular level. On those websites, you may be seeing mineral habits. Mineral habit is the general physical outward appearance of the mineral. Nodular, octahedral, and prismatic are all examples of mineral habit.

To add to that, you should ideally know both. A good understanding of crystal systems is important to understanding the shape of the crystals that the mineral would ideally form - octahedral, cubic crystals are diagnostic of the cubic (isometric) class, but sometimes you'll see crystal shapes that look like they're the result of a mixture of those shapes - for example, a trapezohedral crystal of almandine. However, for identification of minerals based on appearance of not individual crystals, but as a specimen in whole, habit is far more important. It's also easier to use when looking for patterns you can use to ID things.

[dxu46]

I have a kind of similar question, my field guide has 6 types of crystal habits: cubic, monoclinic, triclinic, trigonal, orthorhombic and tetragonal, but on different websites, they list crystal habits like nodular, octahedral, and prismatic and I'm very confused about the difference between these??

Does anybody understand this? Thanks!!

Hey! Another MO user!
Your field guide is correct, but incorrect in it's wording. Cubic/isometric, Monoclinic, Triclinic, Trigonal/Hexagonal, Orthorhombic, and Tetragonal are crystal systems, like kate! pointed out above. Nodular, Octahedral, and Prismatic are examples of crystal habits. Crystal habits are different than crystal systems: for example, a piece of Quartz could crystallize into the Hexagonal crystal system, while it could also be Prismatic and Bladed.

Here are some good websites for both habits and systems: (Click to Show Hidden Text)

(ranked from most useful to less useful, my opinion)
[b]Habits:[/b]
galleries.com/minerals/property/habits.htm (I recommend this one because of good, clear, and readable descriptions and pictures)
minerals.net (3D crystal atlas)
webmineral.com/help/Habits.shtml#.WrgXni7wbX4 (Less description, no pictures, but has more habits then any other website)
en.wikipedia.org/wiki/Crystal_habit
britannica.com/science/mineral-chemical-compound/Crystal-habit-and-crystal-aggregation (Basic info)

[b]Systems:[/b]
en.wikipedia.org/wiki/Crystal_system
gemsociety.org/article/mineral-habits/ (Good diagrams, examples)
gemologyonline.com/crystal_systems.html (Good diagrams)
crystalage.com/crystal_information/seven_crystal_systems/ (Note that trigonal and hexagonal are counted separately)

[Eureka314]

How do you usually ID sphalerite? I feel like I've seen so many different versions of it that it's hard to differentiate

[dxu46]

How do you usually ID sphalerite? I feel like I've seen so many different versions of it that it's hard to differentiate

Sphalerite usually has low hardness and unique dodecahedral cleavage.

[fabishkf]

adamantine luster and 6 perfect directions of cleavage (forming a dodecahedron). The streak is pretty interesting also, but you probably won't have a streak plate on the test (and you don't need it anyway because of the other properties). It's fairly soft (3.5-4) also. So even though it does have a huge variety of crystal habits, there are some distinct properties you can use to identify it.