I often wonder, what exactly IS a tantalum resistor? :^)
There are many "authoritative" answers on the web, not all the same. Qvortrup says the original AN tants were tantalum oxide. "Metal oxide" is usually a dirty word in audio circles, but I've not found any other reference to tantalum oxide. Wikipedia lists cermet (conductive metal ceramics) as including "tantalum nitride (TaN), ruthenium oxide (RuO2), lead oxide (PbO), bismuth ruthenate (Bi2Ru2O7), nickel chromium (NiCr), or bismuth iridate (Bi2Ir2O7)". Tantalum nitride is highly resistant to corrosion in a moist environment - the normal non-audio reason to use it.
All these materials are used in metal film resistors (most often NiCr, applied with several techniques on cylindrical insulators and laser-cut in a spiral pattern), thin-film (sputtered onto a flat surface and etched to trim), and thick-film (mixed with powdered glass and glue and screened onto a surface). These types can range from excellent to total crap for audio purposes; a tantalum oxide bulk-film resistor would be a poor choice!
Bulk foil is usually given first place; there are 3 or 4 alloys used but I've never seen anything about their composition or whether they use any tantalum at all.
Choice of material often depends on the desired resistance, so you may find some resistors that are TaN in a certain value range but other materials in other resistance ranges. All I ever see from suppliers is "these are Magic Tants - give me your money!" so I'm never sure what they actually are.