Mill balls and “lonsdaleite diamonds”

As I note elsewhere, meteorites are not spherical. Nevertheless, I receive many photographs of spherical objects that people think might be meteorites. Here I discuss two special related cases of spherical meteorwrongs – mill balls and objects sold on the internet as “lonsdaleite diamonds.”

Mill or grinding balls

A common way of grinding and pulverizing solid material is with a ball mill. The mill is a hollow cylinder filled with the material to be pulverized along with hard spherical balls. The cylinder is rotated, which cause the balls to tumble and reduce the grain size of the solid material by impact abrasion. Mill balls are made of a variety of materials such as steel, tungsten carbide, glass, plastic, aluminum oxide (alumina) ceramic, and zirconium oxide or silicate.

Photos of mill balls that I found on manufacturers’ web sites. Note that not all are perfectly spherical.

A number of persons have sent me photos of spheres, often found in rivers, that are likely discarded mill balls.


Lonsdaleite is an allotrope of carbon with a hexagonal crystal structure (unit cell). It is sometimes called “hexagonal diamond” but this moniker is misleading and technically incorrect in that diamonds have a cubic crystal structure. (Analogy: If it has a hexagonal crystal structure, then it is not table salt because sodium chloride has a cubic crystal structure.) Lonsdaleite was first found in iron meteorites where it occurs only as rare microscopic crystals, usually less than a micrometer (0.00004 inches) in size. It has also been observed in association with graphite and diamonds in ureilites.

A number of persons have told me that they “see” lonsdaleite in their rock, so the rock must be a meteorite. There are two problems with that logic. (1) If you can see a crystal without a microscope, then the crystal is too big to be lonsdaleite. (2) Lonsdaleite can only be identified by determining that it is composed of carbon and proving that it has a hexagonal unit cell. That would require, at least, identification by x-ray diffraction. It cannot be done by eyeball.

“Lonsdaleite diamond”

At this writing, one can do internet searches for “lonsdaleite diamond” or “lonsdaleite hexagonal diamond” and find alumina mill balls being sold for prices ranging from $20 to $195,000 apiece. OK, the high priced one was actually advertised as a “Lonsdaleite Meterorite [sic] Diamond” and it was rather large at 2.5 inches in diameter. (Free advice: If meteorite is misspelled, then it is probably not a meteorite.)

Ceramic mill balls offered for sale as lonsdaleite diamonds at the Tucson Gem and Mineral Show (2024) (on the left, next to a box of geodes). The person who sent me the photos said, “All dealers were insistent that it was Lonsdaleite diamond, but couldn’t explain how they knew.” One dealer “explained that they were very rare”. The photographer noted that “It looks like a nest of turtle eggs (which are, perhaps, rarer).”
Another display of mill balls at the Tucson show. The text on the right appears to have been taken from Wikipedia. Note that there is no explanation of how the “microscopic crystals” are related to the large white spheres.
My correspondent from the Tucson Gem and Mineral Show said, “The prices ranged from $15 to $100.” I stole this photo and adjacent text above from a sell-buy website. If the photo is that of a kilogram of mill balls, then the per-each price is about $0.50. One can see that selling such objects as lonsdaleite diamonds with “life-force energy” can be a lucrative business.

A fellow identifying himself as a “researcher in particle physics” sent me photos in 2023 of a marble-sized white sphere that he said had been found in Ohio. He identified it as a “meteorite of the name Lonsdaleite Diamond.” I politely told him that it was not a meteorite but that it was a man-made ceramic sphere. He replied “This celestial object is lonsdaleite. I’m sorry for you, your judgments are clearly missed. It is not a ceramic sphere, it has a lot of carbon which exceeds the natural diamond. Revise your words.” 

No, I will not. But I will say this again:

If it is spherical and whitish, then it is not a meteorite, it is not a diamond, and it is not lonsdaleite.