17th
March
2008
St. Patty's Day Deskcrop GeoPuzzle
posted in Geology, Photography, deskcrop |For Spring Break I get to clean up the rock storage room (yay!). So let’s see how many of the following green deskcrops you can identify! Main credit for identifying the green rock/mineral(s) – extra credit for the localities. (Click on each image for a larger view.)
[UPDATE: Final answers are posted!]
 Deskcrop #1 – Olivine-rich sand From near Ka Lae, Hawaii Sample ID and Locality Winner: Callan Bentley |
 Deskcrop #2 – Epidote-rich Blueschist from the Rand Schist, near Randsburg, California Green Mineral ID Winner: Callan Bentley |
 Deskcrop #3 – Eclogite Adula Nappe, Italian Alps Rock ID Winner: Callan Bentley Mineral ID Winner: Silver Fox |
 Deskcrop #4 – Dunite Val Sesia, Ivrea Zone, Italian Alps Rock ID Winner: Chris (GoodSchist) Mineral ID Winner: GeologyJoe Locality ID Winner: Kim Hannula |
 Deskcrop #5 – Charnockite (OPX-bearing granite) near Canada Lake, Adirondack Mts., New York |
 Deskcrop #6 – Slate Metawee Formation, Taconic Slate Belt, Vermont Rock ID Winner: Chris (GoodSchist) Mineral ID Winner: GeologyJoe Locality ID Winner: Kim Hannula |
 Deskcrop #7 – Green Quartzite – fuchsite (Cr-mica) near Sault Ste. Marie, Ontario, Canada Rock ID Winner: Callan Bentley Mineral ID Winner: Silver Fox |
 Deskcrop #8 – Epidote from a skarn in the Old Woman Mts., California Mineral ID Winner: Silver Fox |
 Deskcrop #9 – Wollastonite-Garnet-Diopside Skarn Willsboro, NY Rock & Mineral ID Winner: Kim Hannula Locality ID Winner: Kim Hannula |
 Deskcrop #10 – Amphibolite Green Mineral ID: Chromian Pargasite Seiad Ophiolite, Klamath Mountains, California |
May the luck of the Irish be with you!
Is no. 7 amazonite?
Deskcrop 4 looks like a mantle peridotite. Locality: the mantle
Deskcrop 6 looks like a green slate.
And deskcrop 7 almost looks like serpentine of some sort – but I maybe imagining things. Is it greasy to the touch?
Ron, this is a great idea for a puzzle! (It took forever to load up on my screen, though…)
My tentative IDs:
#1 — Green sand (olivine) from Hawaii
#2 — Epidote & quartz vein
#3 — Eclogite (Adirondacks?)
#6 — Greenschist (Catoctin Fm., Blue Ridge?)
#7 — Green quartzite
#9 — Chlorite / garnet skarn?
#10– Unakite (VA Blue Ridge? — only locality I know for it)
Thanks for the challenge!
I’ll guess the following:
1) olivine
epidote
2) epidote
3) actinolite
4) garnet
5) garnet
6) talc
7) talc
9) chlorite
10) chlorite/actinolite?
1) garnet
2) tourmaline
3)chlorite
7) garnierite, the nickel silicate, from the Mother Lode/Sierra Nevada foothills, a weathering product more or less.
Hi Ron,
Are you still there?
Ok, here’s the best I can do.
1) Only place I’ve seen pretty green rounded sand like that is in Hawaii, so olivine rich basaltic sand.
6) Slate, maybe even a little metamorphisms (phyllite) because I see little flecks in it.
7) Doesn’t look like serpentine to me (I don’t remember serpentine “fracturing” like that), I’d guess more along the line of Callan’s guess of green quartz.
9)Quartz, Garnet, Biotite, but there is also a little tiny green mineral in the quartz. Maybe its a pyroxene, fluorite or tourmaline?
The rest I don’t have very good guesses at. Lots of green minerals here, so that should help narrow it down for most people. I’m going to go look at some sandstones to make me feel better now
Ill give it a go:
quartz syenite
1)olivine/epidoite sand
2)epiodoite
3)ecologite
4)olivine with biotite?
5)syenite
6)slate -chloroite for green
7)quartzite
9) garnet, quartz olive
10)chlorite
please excuse the spelling.
[Authorship corrected - RS]
7) prehnite, Virginia
10) fuchsite
3) a green pyroxene
Omphacite.
7) fuchsite Cr-mica
On the dunite sample’s source;
The best sample of this kind of peridotite I’ve seen was from (I believe) the Skaergaard (had to look the spelling up) complex in Greenland. It remains one of my favourite rock samples. It looked remarkably similar to the sample pictured above, so that’s my guess for source locality.
Of course, I’m sure a quick drive to Stillwater in Montana (thank you Wikipedia) would have been an easier expedition, but I’m sticking with Greenland.
On #4, the dunnite, we agree there is some olivine in there. I’m going to say the other bright green mineral is diopside, possibly with Cr.
9: Garnet + diopside, with wollastonite in the layer at the bottom, from… darn it, it’s a town on the west side of Lake Champlain, at the edge of the Adirondacks.
The eclogite in #3 looks like Franciscan stuff, from northern California, maybe near Jenner?
And I could always guess Vermont (Taconic Mtns) for a green slate.
#5 looks a little like some peridotite that I’ve got from the Alps, but it doesn’t look quite as deformed.
OK, I’m skimming the list fast, but I don’t see anyone guessing “GABBRO” for no. 5
#10) The mineral could be tremolite or actinolite. possible hyrdothermal alteration (greens to orange-ish.yellows) I KNOW I have seen this rock before. I just cant’ nail it down.
For #10: Geez. Do you have any idea how many green amphiboles there are? (Actually, I bet you do
.) How about… ummm… riebeckite? (Is that green in hand sample? I’ve mostly seen the composition written.)
And 5: anorthosite?
Number 5: Ophicalcite perhaps from Switzerland??? Very wild guess…
Riebeckite is usually blue.
10) Mariposite shist.
5) You gave the location as Val Sesia, Ivrea Zone after Kim thought it might be a peridotite. Possibly an eclogite with jadeite, minor garnet, and possible clinozoisite. I also think it could have some kyanite in it, but possibly that’s just the reflective lighting.
Texturally, it looks like a meta-diorite to me.
A better guess for #5 is pyroxenite I think.
And #10 is…dunite…same location as #4 maybe? they both look pretty well pressured to me
Sorry, I meant #10 is same location as #5 not 4.
Well, #7 could be from Greenland, among several other places (Brazil, India…).
Boy, I go away for a day and I’m way behind on replies! (I like this sort of problem!) I think, though, that it’s time to release an answer key. Thank you all for the comments!
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[...] St. Patrick’s Day! I have something of a tradition of celebrating this holiday in rocks, so it should come as no surprise that I saved a green sample for today’s deskcrop. [...]