Is calcite UV reactive
Calcite may fluoresce red, blue, yellow and more under shortwave and longwave UV; it is the only one of 176 reference sheets with five kinds of luminescence.
Is calcite UV reactive? Often, not always. The Handbook says calcite, CaCO3, hardness 3, may fluoresce red, blue, yellow and other colours under shortwave and longwave UV; of the 176 sheets in this site's reference set it alone records five kinds of luminescence. Pure calcite does not glow: manganese makes it red.
In short
- The sheet says may. The Handbook of Mineralogy line for calcite reads May fluoresce red, blue, yellow, and other colors under either SW and LW UV; phosphorescent, cathodoluminescent, thermoluminescent, rarely triboluminescent. A calcite that stays dark under a lamp is still calcite.
- Five kinds of glow, on one sheet in 176. Counted across this site's reference set, ligature-aware: fluorescence on 31 sheets, phosphorescence on 8, triboluminescence on 6, cathodoluminescence on 4, thermoluminescence on 3. Calcite is the only sheet in all five lists; fluorite is in four, and aragonite, baryte and magnesite in three.
- Manganese is the activator for red. The Sterling Hill Mining Museum page on fluorescence says calcite in its pure state does not fluoresce, but with a little divalent manganese (Mn2+) it fluoresces red. Lead acts as a coactivator, absorbing ultraviolet that calcite absorbs poorly and passing it to the manganese.
- Not every glow is the calcite. The same source attributes the white fluorescence of much cave calcite to organic inclusions, and some green from calcite coatings in the Franklin and Sterling Hill district to microscopic opal, not to the calcite. Iron, nickel and cobalt are named as common quenchers.
- Within the calcite group, 3 of 5 sheets record fluorescence. Calcite, magnesite and smithsonite do; rhodochrosite and siderite record none. Lamps and safety are covered on the site's fluorescence pages, not repeated here.
| Species | Fluorescence | Phosphorescence | Thermoluminescence | Triboluminescence | Cathodoluminescence | Kinds |
|---|---|---|---|---|---|---|
| Calcite | May fluoresce red, blue, yellow, and other colors under either SW and LW UV | Phosphorescent | Thermoluminescent | Rarely triboluminescent | Cathodoluminescent | 5 |
| Fluorite | Fluoresces blue, violet, green, yellow, red under UV | May be phosphorescent | May be thermoluminescent | May be triboluminescent | Not recorded | 4 |
| Aragonite | Fluorescent red or yellow under LW and SW UV | Phosphorescent | Not recorded | Not recorded | Cathodoluminescent | 3 |
| Baryte | May fluoresce cream to spectral colors under UV | May phosphoresce | May be thermoluminescent | Not recorded | Not recorded | 3 |
| Magnesite | May exhibit pale green to pale blue fluorescence under UV | Phosphorescence under UV | Not recorded | Triboluminescent | Not recorded | 3 |
Is calcite UV reactive? The sheet's words, and the count
The Handbook of Mineralogy sheet for calcite records calcite as possibly fluorescent in red, blue, yellow and other colours under both shortwave and longwave ultraviolet, and as phosphorescent, cathodoluminescent, thermoluminescent and rarely triboluminescent. Fluorescence is the glow while the lamp is on; phosphorescence continues after it goes off; the other three are light from an electron beam, from heating and from striking or scratching.
Method. The 176 sheets in this site's reference set were converted with pdftotext -layout and searched case-insensitively for each word stem. Many older sheets set fl as a ligature that extraction turns into a stray glyph, so fluorescence was matched as fl or that glyph followed by uoresc. Hemimorphite and willemite, both printed that way, had to match as positive controls, and did. Fluorescence: 31 sheets, against 21 for a literal search. Phosphorescence 8, triboluminescence 6, cathodoluminescence 4, thermoluminescence 3.
Calcite is the only one of the 176 in all five lists. Fluorite is in four, missing cathodoluminescence; aragonite, baryte and magnesite are in three. The fluorite side is on is fluorite UV reactive, and the aragonite comparison on is aragonite the same as calcite.
Why does calcite glow red? Manganese, with lead helping
Calcite's red fluorescence comes from an impurity, not from calcium carbonate. The Sterling Hill Mining Museum page on fluorescence gives calcite, willemite and wollastonite as minerals that in their pure state do not fluoresce, but with a little divalent manganese fluoresce red, green and yellow respectively.
Lead is the coactivator. The same page says calcite is a poor absorber of ultraviolet, so even with manganese present its fluorescence will be feeble; if lead is present as well, the lead absorbs the ultraviolet strongly and passes part of the energy to the manganese, which then fluoresces much more strongly. It names iron, nickel and cobalt as common quenchers, which turn the absorbed energy into a little heat instead of light.
So the answer depends on the specimen's trace chemistry, which no label records. Two calcites from one vein can differ. The Franklin and Sterling Hill district, home of the museum quoted here, is covered on Franklin and Sterling Hill and willemite.
My calcite glows white or green: is that the calcite?
Not necessarily. A glow can come from inclusions or a coating rather than the host. The Sterling Hill Mining Museum page attributes the white or near-white fluorescence of calcite from many caves to molecular inclusions of organic compounds. It says calcite coatings on some minerals of its own district, Franklin and Sterling Hill, fluoresce green, but in some cases the green comes from microscopic intergrowths of opal, not the calcite. Thin willemite and clinohedrite coatings cause spurious green and orange on other species.
- Red or orange-red: the response the source ties to manganese in calcite.
- White in cave calcite: organic inclusions, per the same source.
- Green on Franklin or Sterling Hill material: check for opal or willemite before crediting the calcite.
- Nothing: the sheet's may; no activator, or a quencher, or the wrong band.
Before concluding anything from no response, test the lamp on a known responder. Willemite's sheet reads typically strongly fluorescent under SW and LW UV, which makes it the positive control used in the count above. Lamp choice is on the best UV lamp for mineral collecting.
Which carbonates fluoresce? Three of the five calcite-group sheets
Of the five sheets in this site's reference set whose Mineral Group line reads calcite group, three record fluorescence. Calcite records red, blue, yellow and other colours; magnesite pale green to pale blue, with phosphorescence; smithsonite pale green or pale blue. Rhodochrosite and siderite record none. Siderite is iron carbonate, and the Sterling Hill source names iron as a common quencher; that is consistent with the record, not a proof of it.
Fluorescence is not a test for calcite. The sheet says may, aragonite records red too, and dolomite may fluoresce white to pink. Separating calcite from quartz is on how to tell calcite from quartz; the general background, including the lamp hazards, is on fluorescent minerals explained. The rest is indexed at the collecting guides. Nothing on this site is offered for sale; the wanted list is the only commercial route.