How to Identify Carbonates in the Field

A brief introduction on how to identify some carbonate rocks and minerals in the field, including some that might not react to 10% HCl.
The full video is available in the Fieldcraft for Geologists on-line course here:
geologyupskill.thinkific.com/...
Index:
0:00 Why identify carbonates?
0:40 Carbonate rocks. Karst topography.
0:52 Surface pits.
1:16 "V" shaped fracture traces.
1:51 Porous rind.
2:49 Mosaic fracture pattern
3:19 Recessive layers.
3:47 Palisade texture.
4:13 Carbonatye minerals. Calcite.
5:12 Iron bearing carbonates.
5:24 Siderite
5:55 Ankerite
6:23 Carbonate gossans.
Credits:
Siderite crystal photo: upload.wikimedia.org/wikipedi...
Author: Didier Descouens
commons.wikimedia.org/wiki/Us...

[@SuperMisawo]

Very informative video. The introduction of carbonates that do not react with dilute hydrochloric acid and rocks that were originally carbonates is especially useful.

[@GeologyUpSkill]

Thanks. Hope you find it useful in the field.

[@akshayverma-ue8jl]

Field based study is the best part of the Geology.👍

[@GeologyUpSkill]

Agreed. And now video can share that experience far more effectively than ever before.

[@secretstreamsandfeverdreams]

Wow.. that outcrop at 3.45 was stunning, so beautiful. I grew up climbing barefoot up the local jagged limestone cliffs and I tell you that toughens your feet!

[@GeologyUpSkill]

Yep. Limestone is tough on gear and feet!

[@rhcpalex93]

One of your best yet Nick!

[@GeologyUpSkill]

Thanks Alex. More on the way.

[@nathanbailey3810]

awesome video nick! im studying geology at uwa at the moment, keen to see u out in the field in a couple years!

[@GeologyUpSkill]

It's a great time to be a geologist :)

[@mohs7234]

Hi Pal From Arizona.
Think you just answered my question I asked in the secondary copper about a yellow stone I polished.
That distinctive mustard yellow shade.
Thanks for you informative knowledge!

[@GeologyUpSkill]

There are a few secondary minerals of value with yellow ochre coulours (bismuth, antimony and molybdenum in particular), but the vast majority of mustard-brown powdery secondary minerals are goethite and jarosite after carbonate minerals.

[@leonardomascarenhas9107]

Thaks for posting this video, excelent!!

[@GeologyUpSkill]

Thanks very much. Glad you found it useful.

[@johnnytarponds9292]

Fantastic! Thanks for this!

[@GeologyUpSkill]

Thanks. Glad you found it useful.

[@tectonicrxs]

Excellent video

[@GeologyUpSkill]

Thanks. Glad you liked it.

[@phaithoonvongsinery893]

Very good explain​sir

[@GeologyUpSkill]

Thanks.

[@nuel19]

Thanks you mister

[@Coltbreath]

Thanks Again! Cheers!

[@GeologyUpSkill]

Thanks again for your comments!

[@infinitygeospatial1972]

Thank you

[@GeologyUpSkill]

You're welcome. I hope it helps to improve your field observations.

[@alishafipourgeologist4520]

Excellent

[@GeologyUpSkill]

Thanks Ali.

[@AleksPetrovProspecting]

Hey Nick, can you please explain how identifying carbonate rocks can be beneficial for Gold prospecting?

[@GeologyUpSkill]

The host skarns, mantos and carlin style deposits. They are some of the best gold deposits :)

[@user-pw5sk4sr8c]

I found large-scale molten limestone, which is deposited limestone melted at high temperature, and then cooled and solidified limestone. I judged that it was formed by asteroid impact, and there are the impact breccia on the hills near the limestone.Would love to share my discovery of these rocks with others, you can see pictures of these rocks in the community thread on my channel.

[@GeologyUpSkill]

Great way to start making your own videos. I have a video on how to do that here: ruclips.net/video/ENOslkR0BwI/видео.html

[@user-pw5sk4sr8c]

@@GeologyUpSkill OK，I will try.

[@danielsumomba8696]

Fantastic

[@GeologyUpSkill]

Thanks very much Daniel.

[@matheusviolante8364]

Excellent video! Really liked the comments on the different carbonate minerals at the end! I have just a few questions.
Do you use both 10% HCl and concentrated HCl? Because when you pour over calcite it fizzes like crazy. Either you were using more concentrated HCl or the every 10% HCl bottle I ever got to use was crap hahaha
Also, do you believe Alizarin red to be useful in the field? I tend to overcarry tools, but I feel that chemicals such as HCl and H2O2 are lightweight additions that can help extract much more information when mapping. Wanted to know your opinion, though!

[@GeologyUpSkill]

I only carry 10% HCL. Those little bottles are pretty leak proof, but the occasional escaped drop still wrecks a shirt from time to time. Concentrated HCL is just too dangerous to have in your pocket. The other things are useful if you are on a project with specific needs (for example if you are looking for oxide zinc), but otherwise, the mineral properties are enough for me to raise suspicion and then test for certain at the lab.

[@mantie7]

@@GeologyUpSkill I usually use a double or even triple barrier "system" with higher concentrated HCl. But because of that i only use it very occasionally 😅

[@muzikhed]

That last rock looked like a volcanic scoria rock to me. ....Interesting video, you sure know your stuff.

[@GeologyUpSkill]

Thanks. The weathering surface of sandy carbonates can closely resemble scoria, particularly when the carbonate has some iron or manganese to stain everything dark brown or black. The sudden transition to a grey core is a giveaway for carbonate.

[@mantie7]

Just wrote my exam about hydrogeology in karst. I think it has to be my favorite field

[@GeologyUpSkill]

If you love karst topography, you must visit Laos and it's neighboring countries. The karst exposures are spectacular.

[@BWowed]

Fantastic video. I have found something in Wyoming that nobody has Been able to identify. Do you have any suggestions on how I can find out what it is?

[@GeologyUpSkill]

If it is a mineral, I recommend mindat.org their website has an excellent gallery of images for almost every mineral.

[@crohkorthreetoes3821]

Learning fast enough to almost make my brain hurt, lol

[@GeologyUpSkill]

Hurts so good!

[@rodbhar6522]

I find basalt exhibits similar weathering patterns to these ones you've shown, especially a rind.

[@GeologyUpSkill]

Better put some acid on it then. Perhaps it is carbonate altered!

[@rodbhar6522]

@@GeologyUpSkill Hmmm...never thought about that. The white weathering rind on these basalts from Newfoundland seems to be caused by burial in acidic soil.

[@muhammedsamius9175]

Thanks a lot for the video, if we can add it in the subtitle, it can appeal to a wider area. Best regards.

[@GeologyUpSkill]

If you turn on "Closed Captions" in RUclips, you will get auto generated subtitles. They are pretty good despite my Australian accent!

[@BokandaFrankline]

Professor, thank you so much for sharing this vital knowledge, please if you may help out with Silcretes and silicate rocks in the field

[@GeologyUpSkill]

Next time I see some I will make a video.

[@rajp9928]

Geology Msc degree completed l job training Sir Please Help me

[@johnnynephrite6147]

if you don't have a bottle of acid, some vinegar will sometimes do the trick.

[@GeologyUpSkill]

That will work, particularly if you scratch the carbonate before applying it. And it won't burn a hole in your shirt!

[@iNikhilPant]

We call that weathering “ elephant skin weathering “

[@GeologyUpSkill]

That's a neat way to remember it!

[@donaldkasper8346]

Ankerite is not a common carbonate. I find it exceptionally rare, in very specific locales and rock types, and invariably dark calcite is just calcite in infrared, even black calcite, and is almost never ankerite. Ankerite is not dark, its crystals are pink.

[@GeologyUpSkill]

Most of the ankerite I have seen is in hydrothermal veins and breccias. I might have a biased view since I tend to work on hydrothermal ore systems most of the time. As you say, colour is a very poor indicator of mineral species, particularly for carbonates. The most useful indicator l find for ankerite is that rapid development of an iron oxide surface stain after cutting.

[@donaldkasper8346]

@@GeologyUpSkill Essentially 100% of my presumed ankerites as very dark scalenohedral structures in geodes and other volcanic rocks scan in reflectance infrared as calcite. I can tell the carbonates apart in infrared. It takes very specific and rare conditions for me to see it. For example, the Moroccan black brecciated nodules. Typically in things like Midwest saddle rhomb structures in sedimentary geodes and no place else.

[@donaldkasper8346]

My interest is volcanic agates, jaspers, and opals. These map into ore occurrences all the time. If it is banded agate with silver then I study it as banded agate. For example, other vein lode outcrops of the Calico silver deposits. Given that, the lack of ankerite was very startling to me, and the absolute lack of dark calcite scalen and rhomb structures being ankerite is nearly absolute. My classification keys are for feldspars, all the silicas, the opals (more silicas of course), sulfates, phyllosilicates, the carbonates such that I see 13 species of opals including species like opal-BC (opal-beta-cristobalite) and mixed species like opal-BC-CT, opal-CTA, and so on. I can see mixed carbonates. The agates I call calcsilica rocks as the silica deposition is strongly related to alkaline conditions set up by carbonate occurrence. And if the acidic rocks are around, they react with carbonates to form sulfates with the silica, so on a fine mm scale still form in alkaline conditions. For me, gossan caprocks are jasper occurrences. They occur in hydrothermal vents, along faults, fault offsets of water entrapment, etc, not dissociated from what ore geologists would hunt for. I just hunt them for specimens, not ore to crush and soak in acid, but the search is the same.