FMF - Friends of Minerals Forum, discussion and message board

[Forrestblyth]

My recently acquired calcite specimen behaviour under UV is confusing me.

It glows a very strong bright yellow. It also continues to glow for 3 seconds after UV exposure. Most of my other calcites glow red. there appears to be an additional secondary white crystal present and I am wondering if this is the cause of this strong reaction. But I don't see the normal red colouration I would have expected from the main bulk of the specimen that I am used to from calcite. I am confused why this is so.
The very strong yellow reaction does not seem to record on my camera well yet it is extremely prominent to the eye.

I have tried to capture a few shots of the secondary crystallization but it's very small and is a challenge for my photography skills

The specimen measures about 100mm x 50 x 20

The main diamond shaped calcite crystals measure about 5 to 7 mm and the unknown white secondary crystals are about 0.5 mm.

[Peter Megaw]

Calcite has a very wide range of fluorescent responses stemming from a wide range of trace amounts of activators and sensitizers. This is a VERY deep rabbit hole you have headed down...

The orange-red-pink you are used to seeing is caused by manganese (orange activator) and lead (red sensitizer). That you are accustomed to this suggests many of your calcites are from high temperature hydrothermal base and precious metal deposits (veins, replacements, porphyries).

But calcite occurs in an almost infinite variety of geological environments where different activators may be present. Mercury for example causes a strong blue-white fluorescence with extremely persistent fluorescence when the UV source is removed (also called phosphorescence). There are some localities, like Terlingua, Texas where the calcite fluorescence lingers for up to 30 seconds.

Organic materials can also provoke fluorescence, most commonly in oranges to creamy yellows or off-whites. These also can show persistent fluorescence, but generally it only lasts a few seconds.

Your piece comes from Nanisivik...this is a Mississippi Valley Type deposit, formed from low temperature "oil field" brines. This means the fluids carried plenty of organics, which are probably what is causing your fluorescence.

[Peter Megaw]

Sorry, misread locality...not Nanisivik so forget MVT

These Indian deposits are hosted in basalts...so different source and explanation, but still one of hundreds of calcite environments and fluorescence sources

[Jordi Fabre]

I fixed (again) everything for you.

'Remember that if you are publishing a photo of a mineral specimen please fill in all 3 of the above fields'

[Forrestblyth]

[Bob Carnein]

Nashik produces many minerals that are candidates for the tiny white crystals. It's unlikely that they have anything to do with the yellow fluorescence of the calcite. Unfortunately, the photos don't show the white crystals clearly enough for a useful guess. They appear to be somewhat bladed, which eliminates some things.

As Peter noted, the fluorescent response of calcite is complex and pretty varied. A "bright" yellow response would be rare, from my experience. But creamy yellow is quite common, as is persistent luminescence.

[Joseph DOliveira]

[Forrestblyth]

[Forrestblyth]

P1019274.JPG
Mineral: Calcite on Mordenite

Thank you for the Mordenite photograph. Interestingly, the large specimen box selection this item came from had examples of Mordenite in the box. I did buy one I and I will look to see if it has uv similarities to the secondary material on my specimen

[Bob Carnein]

Some of the white minerals seem to radiate from a central banded material. That may be quartz crystals on an agate core. I would try the hardness (should scratch a knife blade).

[Joseph DOliveira]

To me the white crystals look like bladed stilbite, which would be a common associated mineral from that area. Very difficult to accurately identify from the photograph.

[alfredo]

I agree with Joseph that the little tabular white crystals are stilbite.