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Identity HelpPossible lamproite/kimberlite with spessartine garnet and diamond ?

22nd Sep 2020 08:06 UTCLaura Ebertshaeuser

Hello I recently moved onto a new property in the California. Mother lode . I work locally as a gold mine exploration geologist and have collected many kinds of mineral specimens in the field for many years . I came across an outcrop of blue ground with a yellow halo similar to a small iron hat and has a decomposing granite contact .. I Know many minerals exhibit trigons but I have not seen this particular stepped nature of inclusions along with trigons . It looks like a deposit of orange garnets in quartz with a but the quartz Doesn’t seem quite right ? . This material is also emitting a yellow green fluoresce under short wave UV light

22nd Sep 2020 08:24 UTCKeith Compton 🌟 Manager

From what we can see it could be a burnt circle left by a Martian spaceship as it left Earth! ((-:) ..

i.e.: a photo would help a little bit.

22nd Sep 2020 08:24 UTCLaura Ebertshaeuser

Here is another photo of some of the bigger garnet

22nd Sep 2020 08:31 UTCLaura Ebertshaeuser

I know I’m replying to myself my appologies I was unsure about loading some photos and wanted to make sure you had a clear image i in no way plan to make money and would love to document this deposit there are other garnets deposits near here .. I know nothing about diamonds but do know there have been some found near here Thank you for any attention you can give to the matter

22nd Sep 2020 08:42 UTCKeith Compton 🌟 Manager

Garnets - can be a range of colours. You need only look at the Grossular page: Brown, orange, red, yellow, green, white, colorless .

I don't see any lamproite/kimberlite /diamonds in your photos

22nd Sep 2020 08:59 UTCAlfredo Petrov Manager

The strange markings on the garnets look like contact lines, where the garnet interacted with a neighboring garnet it grew up against.

22nd Sep 2020 10:07 UTCHerwig Pelckmans

Hi Laura,

Welcome to Mindat! Since you are a gold mine exploration geologist, you've come to the right place: Mindat is a gold mine of information about minerals and mineralogy!

You are right, the orange-brown crystals on your specimens are garnets for sure. What species can not be determined on a photo, not even with the naked eye. Since you know the exact locality they were found in California, I suggest you check Pemberton's book (Minerals of California). If you don't have the book, let us know what area this was found, and I'll check for you.

Regarding the greyish crystals in your last photo: these could be garnet too, or something else.

We need photos where we can see the crystal faces of these grey crystals better.

Please be as good/clear as you can in your observations and descriptions. What material is fluorescent under SW UV, and what color do you see? Are any of the crystals fluorescent, and if so, completely, or zoned? Or is it just a thin superficial layer that is fluorescing green?

Cheers, Herwig

ACAM & MKA (Belgium)

22nd Sep 2020 17:41 UTCNick Gilly

The pale colour where the contact lines are suggests grossular is the most likely species.

22nd Sep 2020 18:54 UTCAlfredo Petrov Manager

I agree with Nick that grossular garnet is the most likely candidate. As you live in the Mother Lode area, you can find some surprisingly pale colored and fluorescent (which is very unusual for garnets) grossulars in the Georgetown district of El Dorado county.

23rd Sep 2020 04:50 UTCIan Nicastro

Definitely Grossular Garnet as the others said... but I would like to add that this is classic California skarn material. There are deposits like this all up and down the state, and some of these deposits were worked for tungsten ore (scheelite) in the past. I've found the scheelite crystals are usually rather small and a UV light helps to identify them because of their bright bluish white fluorescence. Calcite and epidote are also common in these deposits, sometimes quartz crystals, diopside, etc... Some folks use acid to etch the calcite away to reveal garnet lined vugs, but read up on the safest way of doing that if you decide to go down that route.

24th Sep 2020 00:03 UTCLaura Ebertshaeuser

Thank you everyone for all the great information most of my knowledge is with hold in Quartz . These stones have an orange color .sorry for the poor photos as my phone is a dinosaur

24th Sep 2020 00:13 UTCLaura Ebertshaeuser

This is the contact not quite greenstone but definite metabasalt .garnets are very orange to peach in color I will send one more photo and thank you for all of the replies this is great .. I’m located in the fair play mining dist. There are garnets near here at the consumnes mine but not quite the same more like the garnet and epidote you would find at garnet hill .these are orange and very brilliant inside .. mica ?

24th Sep 2020 00:17 UTCLaura Ebertshaeuser

One of the larger garnets on the contact . .a couple were loose and in a kind of yellow mud You would normally find in a Vug I have just barely exposed what is here . It appears to run down the side of the hill more found down on the road .

24th Sep 2020 01:16 UTCLaura Ebertshaeuser

This is a Pc of very soft blue and yellow fmground thank you for.the info it is much appreciated they are some very beautiful specimens of garnet mother nature’s gifts I will add them to my collection

24th Sep 2020 09:41 UTCIan Nicastro

I strongly believe you do not have greenstone nor metabasalt. You are in a skarn (feel free to look up this term and learn more about it). A skarn is the product of regional or contact metamorphism. The matrix rock in your photos is a calcium rich metamorphic rock that I believe is referred to as a Tactite and consists of calc-silicate minerals and carbonates and it will start to dissolve if placed in strong acid. The green you see is from microscopic diopside, epidote and possibly vesuvianite. I'm not a geologist but I was informed by other collectors that deposits that produce these orange Grossular Garnets in California were the result of sedimentary rocks like limestone and dolostone (which are calcium-rich) that underwent heat and pressure or were exposed to hydrothermal fluids to yield metamorphic rocks. There is no mica inside your garnets... you are seeing optical phenomena from internal fractures within the Grossular Garnets... these garnets in these skarn deposits often are full of fractures. This is the same geology that is seen at Garnet Hill!

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