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• Materials for Ceramics

Spodumene

Description: Lithium sourcing feldspar

Oxide Analysis Formula Tolerance Li2O 8.01% 1.00 Al2O3 27.41% 1.00 SiO2 64.59% 4.00 Oxide Weight 372.07 Formula Weight 372.07

Notes

The name is from the Greek spodos, meaning burnt to ash. Spodumene is a silicate mineral often referred to as lithium feldspar. Its mineral form is characterized by hard needle-like grains of brilliant white color. It is used in ceramics as a source of lithia.

In ceramics, lithia is a very powerful flux, especially when used in conjunction with potash and soda feldspars. As one of only a few natural lithium source materials, spodumene is a valuable component in glass and ceramic/enamel glazes (Li2O reduces thermal expansion, melting temperature and viscosity of the glaze melt). It was also used in huge quantities to make Corning Ware.

Spodumene is only slightly soluble (in contrast to lithium carbonate). Because spodumene is a natural combination of silica, alumina and lithia it melts better than a chemically equivalent mixture of lithium carbonate, kaolin and silica. Since almost all raw glazes contain kaolin and silica it is normally fairly easy to juggle recipe ingredients, using glaze chemistry, to replace lithium carbonate with spodumene (provided, of course, that the lithium carbonate percentage is not too high). Spodumene can also be substituted for part of the feldspar complement in a recipe without disturbing overall chemistry too much (other than substituting Li2O for KNaO).

That being said, the price of spodumene is increasing rapidly as industry learns to extract the lithium from it. This is being done via calcination to convert the crystal structure from monoclinic alpha (a-form) to tetragonal beta (β-form). Calcination is then further employed in the acid roasting of spodumene, so that lithium can be extracted as water-soluble lithium sulfate.

Some types of spodumene do contribute to the formation of bubbles in the glaze slurry. You can wash spodumene before use to alleviate this issue (mix it well in plenty of hot water, allow to settle overnight, pour off the water the next day and dry it).

Spodumene is a little more readily fusible than petalite since it is higher in lithium. It is considered a better source of Li2O for frits. Some sources quote the percentage of Li2O in molar percent rather than weight percent (resulting in a much higher figure).

Spodumene powder, although heavy, dusts easily and is very unpleasant to smell or breathe. And it sticks to tools, scoops and containers. Good ventilation equipment is essential when working with it.

Related Information

Spodumene ore

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Spodumene ore: Typically refiners want 6% or more LiO2 content.

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Sourcing Li2O from spodumene instead of lithium carbonate comes at a cost

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Lithium carbonate is now ultra-expensive. Yet the reactive glaze on the left needs it. Spodumene has a high enough Li2O concentration to be a possible source here. It also has a complex chemistry, but the other oxides it contains are those common to glazes anyway. Using my account at insight-live.com, I did the calculations and got a pretty good match in the formulas (lower section in the green boxes). Then I made 10-gram balls and did a GLFL test at F (notice the long crystals in the glass pools below the runways). Not surprisingly, this recipe is very runny, that's why the tiny yellow crystals grow during cooling. The new version fires very similar, perhaps better. Our calculated cost to mix this recipe in was $17.84/kg vs. $10.40/kg. But there is a practical cost: Poor slurry properties. The spodumene sources so much Al2O3 that 70% Alberta Slip had to be dropped to accommodate it! How does one use this type of glaze without ruining kiln shelves? Using a catcher glaze is one answer.

Example of a commercial spodumene

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Our theoretical chemistry is fairly close to this (notice these numbers are not precise, they indicate a range or minimum).

Spodumene can bubble when mixed with water.

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This is what happens when some spodumenes are mixed with water. They generate foam and bubbles. This is disruptive in glazes and can be alleviated by washing and drying the powder before use. Or calcining at 500-600F.

Spodumene glaze with natural ironstone concretion speckle

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LA speckle test cone 10R (G spodumene) using ground ironstone concretions (50% 70-100 mesh, 35% 50-70 mesh, 15% 40-50 mesh) at 0.5%, 0.3%, 0.1% (left to right).

Adding spodumene to this floating blue tones down the white patches

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GA6-C (left) and GA6-E (right) at cone 6 oxidation. The E version adds 4% spodumene onto the 4% rutile in the C (the base is 80% Alberta Slip and 20% frit ). The spodumene eliminate the overly whitish areas that can appear. This glaze requires the "Slow Cool (Reactive Glazes)" firing schedule. It looks the best on dark bodies.

A problem with spodumene fluxed glazes: bubbles, surface dimples

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This is a closeup of GB, a recipe with 11% spodumene. Although the glaze is very glossy, its surface is marred by tiny dimples, the remnant of broken and partially healed bubbles escapes. These bubbles were in the laydown and dried in place (the spodumene generates these in the slurry itself, making it frothy). This can be reduced by drop-and-hold firing techniques, but a better answer is to find a frit to source the Li2O.

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Here is why Spodumene powder glistens in the light

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Spodumene ceramic grade, used in glazes, is a 200 mesh material. How could the particles be big enough to glisten in the light? This is a micrograph of some of the particles from the 0.6% plus 100 mesh material that I extracted in a particle size distribution test. And 8% is plus 200 mesh. And all that material is flakey like this, millions of tiny mirrors. This also explains why the material becomes airborne so easily and why it is really really not good to breathe this stuff in.

Here is why Petalite and Spodumene will seldom substitute for Lithium Carbonate

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Of course, if a recipe only calls for 1-5% lithium carbonate either of these might be candidates to supply the Li2O. However, Petalite is eight times less and Spodumene five times less concentrated than lithium carbonate so to make either worthwhile the prices would need to be eight and five times cheaper. But if a recipe calls for more there is another problem: Petalite is extremely high in silica, which means supplying the needed Li2O from it is almost certainly going to oversupply SiO2. Spodumene will likely do the same. Both are also high in Al2O3 and likely to oversupply that (or at minimum supply the bulk preventing the presence of kaolin in the recipe).

Links

Spodumene

lithium aluminum silicate

Pink Kunzite
Photo © Kacpura | Dreamstime.com

Spodumene is a lithium aluminum silicate (LiALSi2O6) and the principle source of lithium, the lightest of all metals. It is a relatively rare pyroxene found mainly in lithium-rich pegmatites. Rough crystals of spodumene have been found in huge sizes, one of the largest single crystals being over 47 feet long and weighing 90 tons.

Spodumene occurs almost exclusively in lithium rich granite pegmatites. It is a relatively rare mineral, occurring in association with quartz, microcline, albite, muscovite, lepidolite, tourmaline and beryl. Spodumene is a new mineral to science, as it was discovered only in the last three centuries; gem varieties have only been known for the past 120 years.

Gem spodumene occurs very rarely and in much smaller crystals ranging from colorless to yellow, pink to violet (kunzite), yellowish-green to medium deep green (hiddenite) and an extremely rare light blue color. The color in these gems is due to impurities substituting for aluminum in the crystal structure -- iron produces yellow to green-colored spodumene, chromium produces deep green-colored spodumene; manganese produces pink to lilac spodumene.

Spodumene is recognized by its prismatic cleavage, crystal habit, striated prisms, color, fracture, and by its pegmatitic occurrence. Gem varieties of spodumene can be distinguished by their strong pleochrism and by their higher refractive index from similar appearing pegmatite minerals such as quartz, topaz and beryl. The stone occurs in California, North Carolina and South Dakota, in the USA; and in Afghanistan; Pakistan; Brazil and Madagascar.

Spodumene is a major source of lithium, which has a great variety of uses including in the manufacture of lubricants, ceramics, batteries, welding supplies, experimental fuels and in anti-depressant drugs. Spodumene gems are perfectly suited for setting into rings, pendants, brooches and earrings. The perfect cleavage of spodumene makes it more difficult to facet, and care is required to prevent damage when wearing a spodumene gem set in a ring.

The name spodumene was derived from the Greek spodumenos, which means burnt to ashes in reference to spodumene's common light gray color. Kunzite was named for the author and gemologist George F. Kunz, and hiddenite was named after A. E. Hidden who was one of the original mine owners of this type spodumene.

Hiddenite

Hiddenite is a deep green spodumene found only in Hiddenite, North Carolina. Both the town and the gem are named after William Hidden, the original mine owner. Hiddenite occurs only in small crystals and is quite rare. Ordinary green spodumene from other localities is often erroneously and misleadingly labeled hiddenite.

Kunzite

Kunzite is the violet-pink variety of spodumene and is one of two gemstone varieties. The other variety is green and is called hiddenite. Kunzite is strongly pleochroic, meaning there is a different color intensity variation when a crystal is viewed from the top or the bottom than if it is viewed from other directions. The top and bottom of the crystal reveal the deepest colors and knowleagable gem cutters take advantage of this characteristic. Due to kunzite's cleavage, splintery fracture and strong pleochroism it is considered a real gem cutter's challenge. However, its lovely pink color makes kunzite an attractive and desirable gemstone.

Traditionally, the wearing of kunzite is thought to bring good luck. The astrological signs of kunzite are Scorpio, Taurus and Leo, and the sign of hiddenite is Scorpio. Kunzite is a birthstone for the month of September.

Kunzite is said to help strengthen the circulatory system, help one understand and interact better with others, to help heal "broken hearts," to relieve stress and anger, and to bring love, peace and harmony. Hiddenite is said to enhance one's creative and spiritual potentials, and to stimulate the intellect.

SPODUMENE CHARACTERISTICS

-- Bob Katz

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