Seashells that Fluoresce

in Ultraviolet Light

Colorful Fluorescent Seashells in Long Wave Ultraviolet Light

Fluorescent Seashells – The image above is an assortment of seashells fluorescing in response to long wave ultraviolet light. These were found using a UV flashlight in my first visit to a large Florida shell store.

The shells above were found in a large Florida Shell shop during a recent vacation in Fall 2021. I took a quick phone photo. Some fossilized shells from Florida fluoresce as described in a recent 2015 issue of Smithsonian magazine and this prompted my search. I also recalled hearing years ago that a few shells fluoresce, but never saw any detailed info or color photos. One of the new bright LED Convoy C8 LW UV flashlights was used to search through the extensive assortment of shells available in the shell stores in daylight. With the older UV lights, it was necessary to be in a dark room to check for fluorescence. The vast majority of shells do not have a fluorescent response.

Since the fluorescent response varies widely from shell to shell, I needed to select them in person with my UV flashlight instead of ordering online. The red fluorescent shells above all come from the Asia Pacific region. Unfortunately, there are not many shell shops remaining in Florida and the shop that had these was closing its storefront in a few weeks. There is still at least one nice shell store in each major beach resort area in Florida. I also checked a large mound of old shells near the Tampa Bay bridge rest area but did not find anything other than a couple of shells with two small yellow dots inside.

In Florida, collection of live shells (i.e., a mollusk is still inside) is not allowed. There is also an annual permit needed to collect fossils in Florida. Most of the interesting and colorful shells in shell stores these days come from the Asia Pacific region. Vietnam and the Philippines export many shells.

The image above shows the same fluorescent shells in normal lighting.

Encouraged by what I found in the first shell shop, a following trip to southeast Florida included a stop at Sanibel Island. I checked the large variety of shells available at Sanibel Seashell Industries and found this collector shell below along with several others. I selected this one that displayed more red fluorescence than the half dozen or so others in the display case. This was the best brick and mortar shell store I have found.

At this shell store and many of the others I visited, I had an interesting talk with the owner, manager, and clerks when they saw me checking out shells with the UV flashlight. The owner at Sanibel Seashells had heard of UV fluorescence from years ago, but the others I met had not. They were all very interested to see what I found. He showed me this specimen shell in one of his locked display cases and we were both surprised by the great red fluorescence and tiny white stripes. Fortunately, LW UV penetrates glass so you can quickly check inside glass display cases without opening them. SW UV is blocked by glass. It is an amazing shell even in normal light and one of my favorites.

A rare Angaria vicdani collector shell with a bright red fluorescent response to LW UV.

Angaria vicdani collector shell in normal lighting

A recent issue of Smithsonian Magazine shows the UV response of fossilized seashells in this article:

https://www.smithsonianmag.com/smart-news/uv-light-reveals-colors-fossil-shells-180954841/

It appears that in many cases exposure to bright sunlight and oxygen for prolonged periods of time enhances the UV response of many seashells such as those found in Florida. This is why fossilized shells found on the surface tend to fluoresce more. So far, no one understands the details behind this chemical process, and it likely involves some trace amounts of organic compounds. The most common color that seems to show up as a result of this process is a yellowish orange.

There are a few interesting, related YouTube videos:

https://www.youtube.com/watch?v=T_HqYfzIHVo shows colorful UV fossilized seashells collected on the land in Florida

https://www.youtube.com/watch?v=4V9TCdCbX6U&t=250s shows UV response of live corals and creatures in the Black Sea

https://www.youtube.com/watch?v=9kmE7D5ulSA shows a recently discovered biofluorescent sea turtle in the Solomon Islands

Here are some additional interesting shell references and resources I found:

Located near Fort Myers, Florida on Sanibel Island, Bailey-Matthews National Shell Museum is the only museum in the U.S. devoted entirely to shells and mollusks. In addition to a large shell collection and live mollusks on display, they have a small UV display of some fossilized seashells from Florida. They also have a guide for Southeast Florida shells and even a phone shell ID App on their website.

Annual Shell Shows are held in several locations and are an excellent way to see displays and purchase a wider variety of shells. The Conchologists of America (COA) maintains a listing of shows and events.

The free online WoRMS (World Register of Marine Species) database is a great reference to check identification, shell names, and find images.

Other Sea Creatures and Fossils

A later trip to Naples included a stop at Kelly’s Shell Shack where I discovered that green Fire Coral has a nice lime green fluorescent response to LW UV. Most coral just fluoresces white, perhaps related to the cleaning process. They also had most of the shells I had found previously.

Fluorescent Fire Coral: The green variety of Fire Coral fluoresces a lime green color in LW UV light. Most white coral specimens have a slight white response. Live corals can be very colorful.

Fire Coral in normal lighting is white with only a faint green color.

Some Fossilized Shark Teeth have a mild fluorescent white or yellow cream color response to LW UV light. The darker teeth collected from freshwater areas tend not to fluoresce.

I arranged my fluorescent shell collection on a shelf with a LW UV light. The lime green fire coral made a great background. At Shell Factory in Fort Myers they even had fire coral on sale, so I added a second piece. I took a quick photo with my phone, but it really needed a better camera with more focus and exposure control to do it justice in UV.

A Shelf with a Seashell and Fire Coral Collection

Fluorescent Seashells and Fire Coral in LW UV light.

Here are some new finds from the 2022 Sarasota Shell Show:

Acteon eloiseae in LW UV, Oman

These shells from Sarasota Exotic Shells have a bright orange to reddish orange, fluorescent response to LW UV. They had an impressive assortment of specimen shells.

Acteon eloiseae in normal light, Oman

Cowries

It seems that Cowries have a nice red fluorescent response for several species found around the world, but the majority exhibit no fluorescent response. The red fluorescent Map (Mappa) Cowrie is one of the first fluorescent shells I noticed. They are widely available in shell stores at a low cost. They are a great fluorescent starter shell for any collection. This was two red fluorescent shells I had heard about years ago, and the others turned out to be a surprise especially the colors other than red.

Mapa (Map) Cowrie in normal light

Mapa (Map) Cowrie in LW UV

This is the first bright fluorescent shell I have found collected from Florida. This small Cowrie is from Pompano Beach a few hundred feet out in the Atlantic. I also saw some in a display entry at the Sarasota Shell Show from Key West that were similar in the fluorescent red response. So far, I have not found shells from the Florida Gulf area that have a bright fluorescence.

Cypraea cinerea in LW UV, Pompano Beach, FL

Cypraea cinerea, Pompano Beach, FL in normal light

Here is another Cowrie from the Mideast

Cypraea Pulchra in LW UV, Oman

Cypraea Pulchra, Oman

This Cowrie from Australia has a very deep red fluorescent color.

Cypraea Zolla Venusta Sorrentansis Cowrie from Australia in normal light

Cypraea Zolla Venusta Sorrentansis Cowrie from Australia in LW UV

Here is a random assortment of different small Cowries I found with a fluorescent response.

Assortment of small Cowries in normal light

Assortment of small Cowries in LW UV

I also tried one of the first new SW UV LED flashlights at the show. It seemed that it was more common to have a bright fluorescent response to LW UV in seashells. That is different than fluorescent minerals where more respond to SW than LW. So far, I have not found a shell with a bright SW fluorescent response. Those that do have some fluorescence in SW are brighter in LW. This may actually be good news for shell collectors. SW lights are more expensive, generate ozone, cause sunburn and eye damage, and can fade fabrics over time. Shells from warmer climates tend to be more colorful in daylight and this also appears to be true for fluorescence in shells.

Angaia Sphaerula in LW UV, Balicasag Island, Philippines

This shell also from Sarasota Exotic Shells has a nice fluorescent response to LW UV. It had a bit of lint on it from the case that shows up as tiny blue streaks or dots. This is a frequent problem when taking UV photos. I cleaned it up as well as I could with a can of Dust-off and took a new picture!

Angaia Sphaerula, Balicasag Island, Philippines

The most recent trip to Florida included the 2022 Tampa Fossil Fest, the Panama City Shell show, and stops at four local shell stores in the area. Here are the new UV finds.

Olives

Two Gold Olives in LW UV

I found these Olives at the Shell Hut Gift Shop in Panama City Beach.

Gold Olives in normal light

Augers

Many of the white Auger shells I found fluoresce yellow to orange.

Auger Shells in LW UV light.

Auger Shells in normal light

Here is another shell with fluorescent orange stripes. It has a very thin shell, and I don’t know the species. I only found one at a shell store with no identification at all and a bit of damage, but it has a nice orange fluorescence in LW UV.

Shell in normal light

Shell in LW UV

These white shells often have a bright bluish-green fluorescent interior in LW UV.

White Stombus Epedromis Shell in normal light

White Stombus Epedromis Shell in LW UV

Scallops

There are a few Scallop shells that fluoresce orange and yellow. These were selected from a large basket at a Florida shell store.

Scallop Shells in LW UV light

Scallop Shells in normal light

Umboniums

Many of the tiny button top shells from Asia have a small red fluorescent dot in the center on the bottom of the shell. In this variety that I found at Daniels Shells, the dot is larger and more colorful than most.

A small dime size Umbonium shell from Asia in LW UV

Umbonium shell in normal light

In shell stores Umbonuim (i.e., button top) shells are often sold by the scoopful at a very reasonable price for use in crafts. This assortment seen in LW UV was less than $1. The shells were hand picked and oriented in the photo to show the bright red fluorescent response.

Here are a couple more Umbonuim assortments randomly scooped up at three other shell stores. They likely come from different locales, contain other species, and they are also even smaller. Some have a white fluorescent response.

Medium size Umbonium in LW UV

Small Unbonium in LW UV

Small White Unbonium in LW UV

Here are some other very small white shells all less than one inch in normal light and then LW UV that fluoresce orange to yellow. No identification was available at the shell store. It is likely several of these are juveniles. In the Peanut shells, I only found three in a bin of a thousand or so that were fluorescent.

Shell in normal light

Shell in LW UV

Peanut Shell in normal light

Peanut Shell in LW UV

Auger Shell in normal light

Auger Shell in LW UV

Tiny Conch Shell in normal light

Tiny Conch Shell in LW UV

Another small shell often found in shell shops is the red Strawberry Top (Clanculus Puniceus). They look even more like strawberries in LW UV.

Strawberry Top shells in normal light

Strawberry Top Shells in LW UV

The red fluorescent areas in these Turban shells varies widely from shell to shell.

Bolma Turban Shell in normal light

Bolma Turban Shell in LW UV

Shell in normal light

Shell in LW UV

These Tusk shells are a faded green in normal light, but they always seem to fluoresce a pinkish red color. Note the tiny drill hole in the bottom one. Wonder what tiny predator does this and was the Tusk shell anchored down in the sand when it happened (it’s likely another snail).

Tusk Shell in normal light

Tusk Shell in LW UV

Clams

I thought perhaps I had found just about every fluorescent shell that was out there until I found this shell at a small gift/shell store that I almost passed by. This exceptionally large file clam comes from deep water in the Philippines. The yellow tint color bands fluoresce a bright yellow green color in LW UV. I have seen three others since then and they all had the bright fluorescent response. It is so colorful, I thought it might be dyed or painted, but the normal light photo of it looks the same in the official WoRMS database.

Lima Dalli clam in normal light

Lima Dalli clam in LW UV

After the new shells I found during the Spring break 2022 trip, it was time to expand and rearrange my fluorescent shell shelf and take better photos using the Cannon 24-megapixel T7 on a tripod. The earlier handheld phone photos with autofocus and autoexposure did not do it justice in UV light. There was not room for the large fossil shells, looks like that will need a new shelf.

Fluorescent Seashell collection in normal light

Fluorescent Seashell collection in LW UV

Fossil Shells that Fluoresce in UV

This white weathered/fossil Conch shell fluoresces light orange in LW UV. I selected this one using my UV flashlight from a large barrel at Shell Port in Panama City to find one with a good orange response throughout the shell. At what point an incredibly old, weathered shell becomes a fossil shell is likely open to debate.

Weathered Conch shell in normal light

Weathered Conch shell in LW UV

Fossil Shells

The Florida Museum of Natural History has a huge display of fossil shells and a wall showing what a cross section of a shell quarry looks like from the Pleistocene Epoch. Admission is free and it is only five minutes off I-75 in Gainesville.

Photo of a Florida shell quarry from https://www.fossilshells.nl/loc_c-fl_table.html

In addition to photos, this site also lists the names and locations of many shell quarries in Florida, but most are likely closed now to the public. At the Tampa 2022 Fossil Fest, several vendors had fossil shells from Florida. Most of them had been collected years ago when it was possible to collect from local shell quarries.

Here are some fossil shells and coral collected years ago from a shell quarry near Lake Okeechobee in Florida. I searched through the large bins one dealer had at Fossil Fest to select those that displayed more of a fluorescent response. Based on what I saw in the considerable number of Fossil shells available there, the theory from one researcher that prolonged exposure to sunlight on the surface may produce an orange fluorescence may well be correct. Most had no fluorescence or just a few patches of orange even in the same species from the same locale.

Large Fossil Clam in normal light

Large Fossil Clam in LW UV

Fossil Conch in normal light

Fossil Conch in LW UV

This is one of the only shells where I have seen a color with a stronger SW UV response. Note the green fluorescent spots that appeared in the upper left in short wave ultraviolet.

Fossil Conch in SW UV

Fossil Rose Coral in normal light

Fossil Rose Coral in LW UV

Fossil Star Coral in normal light

Fossil Star Coral in LW UV

The dealer told me these two fossil whelk shells below were collected near Sarasota in an area that is now full of condos.

Fossil Whelk shells in normal light

Fossil Whelk shells in LW UV

The larger whelk shell with the hole may also be a Native American artifact. In south Florida, workable rock materials like flint were in short supply, so large whelk shells were drilled out with two holes and mounted on a wooden handle to make a hammer-like tool. There are two holes in the shell on opposite sides and the tip is worn down to a chisel-like edge. It could also just be natural damage. Such tools can be seen in several museums, and some have been found with the remains of the wooden handle still attached. For more information on the significance of Whelk shells, see: https://www.researchgate.net/publication/35274267_The_Significance_of_Sinistral_Whelks_from_Mississippian_Archaeological_Sites

Recently, large Mercenaria permagna clams containing honey calcite crystals were discovered at Rucks’ Pit near Fort Drum. Since these clams were found in the hinge-up living position, it is suspected that they died in place due to a catastrophic event, such as freshwater poisoning that could have resulted from a flood from a hurricane. The clams are between 1 and 1.5 million years old. Similar finds have also been made in other areas of Florida.

Photo from Florida Calcite (apalachee-minerals.com)

Fossil Clam from Florida with Calcite inside

Fossil Clam from Florida in LW UV

The calcite from this site inside the fossil clam shells fluoresces a light yellow-green color under shortwave, midwave and longwave UV light. It also phosphoresces for a second or two once after a UV light is turned off. Honey colored calcite from much of Florida has the same response even the calcite found in caves in Florida. There are caves in Florida. A bit north of Panama City a state park even has cave tours and there are some caves near Lecanto just north of Tampa.

Tampa Bay Agatized Coral from Florida often has a fluorescent response inside the cavities.

Agatized Coral in normal light

Agatized Coral in LW UV

Fossils with extensive mineralization such as the previous two, are often also considered fluorescent minerals by those that collect minerals.

Here is another fossil of a sea creature that fluoresces. The remains of the shell on this shrimp fossil fluoresce a pale yellow under LW UV.

Shrimp Fossil from Lebanon in normal light

Shrimp Fossil in LW UV

Here is a calcite mineral specimen from Florida. Like the earlier calcite in clam example, it is also fluorescent yellow to off white in SW UV.

Florida Calcite from Key Largo in normal light

Florida Calcite from Key Largo in SW UV

It looks like just a yellow rock with crystals, but in the closeup below you can see it also contains faint stony coral impressions. So, it appears the calcite was deposited around the rose coral and it all eventually merged into one large piece of calcium carbonate from both sources.

In a closeup view, this Calcite specimen contains the trace patterns of fossil rose coral

Dyed Shells

Some Shells are dyed or pearlized during processing to make them more colorful and many of the dyes used are fluorescent under LW UV. This is a bit more common in shells sold for crafts. At times, it can be difficult to determine if a shell has been dyed or is natural. I have tried to avoid collecting dyed shells even though they can be very colorful in UV.

Here is one I suspect might be dyed or painted inside the shell. The two halves are firmly glued together. I would likely break it, if I open it up to check. I did find some other shells at one store where the glue failed, and one had fallen apart into the two halves. It actually had fluorescent paint on the inside to make it more colorful.

Dyed? Clam Shell in normal light

Dyed? Clam Shell in LW UV

What Causes Fluorescence in Some Shells

UV light causes electrons to temporarily absorb the UV light energy, jump to a higher orbit, and when they return visible light is emitted as seen in the drawing below.

Seashells are primarily composed of calcium carbonate. According to Hare and Abelson (1965) and Marxen et al. (2003), molluscan shells consist of 95-99.9% calcium carbonate and 0.1-5% organic material by weight. The mineral form of calcium carbonite is called calcite. The fluorescence of calcite has been studied for almost two hundred years. Pure calcite does not fluoresce. Trace amounts of other elements in calcite called activators are required for fluorescence. Several fluorescent calcite mineral specimens that fluoresce distinct colors with different activators are seen below. The interior of shells often contains a layer of a less dense softer crystalline form of calcium carbonate called aragonite.

In Calcite mineral specimens different UV fluorescent colors are produced by different activators

The activator can be determined by studying spectral emission data. It also has been confirmed in some cases by making a synthetic version of calcite. This information is summarized in detail in a fluorescence database at http://www.fluomin.org/uk/ in the entry for the minerals calcite and aragonite. Manganese is the most common activator for red and reddish-orange fluorescent calcite. Lead and Cerium may also be co-activators in Calcite with a manganese activator. Both trivalent dysprosium and trivalent samarium are capable of producing orange fluorescence. Organic compounds are suspected in pink and yellow fluorescence, and uranium in green and blue.

In the mineral Calcite, most specimens with red fluorescence with a manganese activator fluoresce stronger in short wave than long wave. Shells seem to reverse this; they are brighter in long wave than short wave. Many shells also have certain regions that fluoresce while others do not.

So, the absence or presence of these trace amounts of activators explains why some shells fluoresce and others do not. Additional spectral emission research is needed for each shell type to confirm which activators are present, and it is possible that additional activators, co-activators, and organic compounds in shells are involved as activators that are not found in the previously studied fluorescent calcite mineral specimens. With over 100,000 mollusk species, details on this chemistry in each one is not likely to be discovered anytime soon. Organic compounds in shells typically consist of proteins and sugars. An interesting short video on how shells are made by mollusks explains this all a bit more: https://www.youtube.com/watch?v=iUeMxjkSPyM

The red fluorescence in most shells is likely the organic material, porphyrin and not manganese as is common in the mineral calcite. Not much seems to be known for sure about other colors in shells. Until I started looking I thought there were only a few red ones.

UV Lighting Options and Macrophotography

Photo of High Output LED LW UV Convoy C8 Flashlight from Engenious Designs

While red LEDs have been available for fifty years, development of high-power UV LEDs with a long life has taken additional years of research and they have only recently been available in shorter wavelengths. New LED-based LW, MW and SW UV flashlights just appeared on the market several months ago that make it much easier to check shells for fluorescence in shell stores and shows. Do not confuse these lights with inexpensive earlier generation UV LED flashlights with a wavelength of 400 nm and many small purple LEDs, the output of these new larger LEDs is significantly higher and at a lower UV wavelength of 365nm. The small difference in wavelength can drastically change or diminish the fluorescent color response. The LW UV flashlights are also available now on Amazon and at a lower cost directly from China, but I don’t have any experience with those other sources.

The high-power LED lights are bright enough to check for a fluorescent response in daylight in a store or at a show. Older traditional fluorescent tube-based UV lights are not as bright or portable. With the older UV lights, it was necessary to be in a dark room to check for fluorescence. There are also new LW UV LED lighting options for permanent displays.

A Low Cost Blacklight based on a fluorescent tube outputs LW UV

Low cost Blacklights such as the one seen above can also be used but they also output a lot of visible purple light in addition to LW UV. Quality UV lights have a special optical bandpass filter to eliminate excess purple light.

LED LW UV Display Light with Filter

The nicest small LW UV display light I have used for permanent displays is the LED-based Linker that has the bandpass filter. A few $12 fluorescent tube Blacklight fixtures from Walmart also work, but they put out quite a bit of visible purple light. This still might be an option for those that leave UV lights on all the time in a display. Current UV LEDs have a life expectancy of something over 2,000 hours. Most museums cycle off UV display lights with a timer for a longer lifespan. Even then, I have been disappointed on several museum visits to see fluorescent displays where the UV light has burned out. This is more critical with SW UV lights since the very expensive filters can also cloud up over time with extensive exposure to SW UV.

How the UV Photos were taken

After struggling to get quality closeup UV photos with my smartphone, I switched to a Cannon EOS Rebel T7 24 mega pixel DSLR camera with the Canon USB remote shooting software, and an AC camera power adapter in a darkened room. Automatic focus and exposure times often don’t work correctly with UV images. The zoom lens came in handy since the size of shells varies. With the remote shooting software, you can see a live preview image on the PC and use it to manually adjust focus and exposure times. A 3X macro close-up adapter and UV (i.e., Sky Fog) filter were added to the lens. UV light is invisible to the eye, but camera sensors often pick up a blue/purple haze in photos from UV. The UV photos require long exposure times of perhaps several seconds. This is too long to be done handheld with a large F stop (i.e., maximum depth of field for focus), so the camera is mounted on a photocopy stand.

Two 36W filtered LW UV LED 365nm display lights were mounted on a PVC pipe frame above the copy stand facing the shell at opposite forty-five-degree angles to minimize shadows. An LED lighting ring on the camera was used for visible light photos. A black craft foam sheet was used for the background. Most white backgrounds fluoresce white and tend to wash out the UV colors, so flat black works better for UV photos. Tiny lint and dust particles always seem to fluoresce bright blue in UV light and are all but invisible in normal light. Dust-off was used to clean away any tiny dust and lint particles that are bright blue in UV. In some cases, even using Dust-off it was necessary to remove stubborn tiny dust and lint particles from image backgrounds using the free Paint.net software.

Even with the UV filter, sometimes the camera picks up blue from UV and the blue level might need to be reduced just a bit for correct colors. The excess blue can change other colors in photos. Exposure times are also critical, the very bright colors make it easy to saturate the color sensors in camera. I typically take several different exposure times for each photo, and then select the best one after looking carefully at the images on a large monitor. If you have a license, Photoshop is a bit more powerful for serious image editing. Colors and brightness also vary a bit depending on your graphics display and software. I tried to adjust it on my PC display to look exactly like what I saw taking the photos.

Photographic Images © 2022 James O. Hamblen except those as noted in figure captions from other sources. Personal use rights for individuals or educational use rights to photographic images will be granted to schools, museums, and non-profit organizations as long as the original source is cited.