I bought two rods from Aliexpress. They say they are Manganese Zinc. Appearance is coarse and sparkly. Fairly light grey with ligher sparkly bits. Has rough edges, including the flats along the length, so not a full cylinder. Diameter around 9.8mm wide part, 8.8mm on flattened sides. Length around 99.9mm.
These should be the type more suitable for lower frequencies, such as LF antennas which I got them for.
Wikipedia says:
The most common soft ferrites are:[20]
Manganese-zinc ferrite
"Mn Zn", with the formula Mn δ Zn (1−δ) Fe 2O 4. Mn Zn have higher permeability and saturation induction than Ni Zn.Nickel-zinc ferrite
"Ni Zn", with the formula Ni δ Zn (1−δ) Fe 2O 4. Ni Zn ferrites exhibit higher resistivity than Mn Zn, and are therefore more suitable for frequencies above 1 MHz.[22]For use with frequencies above 0.5 MHz but below 5 MHz, Mn Zn ferrites are used; above that, Ni Zn is the usual choice. The exception is with common mode inductors, where the threshold of choice is at 70 MHz.[23]
Where the light is brighter, if the color of ferrite is black and the crystal is bright, the core is manganese-zinc ferrite; if the ferrite is brown, glossy and grains are not bright, the core is nickel-zinc ferrite. Visual measurement is a relatively rough method, which can be mastered through certain practice.
https://www.xfullstartechs.com/info/the-difference-between-nickel-zinc-ferrite-and-39328424.html
Resistance with normal sharp gold multimeter probes pressed into ends of rod went down to 59 M Ohms.
Rod attracts magnets fairly strongly.