orichalcum

Hmm. There's an interesting take in Wikipedia from a Hebrew University professor that suggests a the numerical discrepancy is more a matter of misinterpretation (600 alaphim=600 units, not 600 thousands), in which case the Hebrews might have had ~6000 fighting men and less than ~20000 people total, which becomes within the range of plausibility for 2 midwives.