UA6IBQ

Графен не считаем -)
золото 2360
серебро 5950
медь 6520 6600-7400 USD/тонна
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эх жаль, дороже и горят -)
магний 13100 USD 2400-2800 сплавы до 7тысд
кальций 19200 3400-3800 провод и КМ никто не делал
литий 20200 $6400 / т вырос с 2000 до 7000,... ... УпД торгуют 98%-ным по 35 тыс руб за тонну

УпД: натрий еще круче :-)
размерность другая, правда http://en.wikipedia.org/wiki/Electri...d_conductivity
Resistivity density products

In some applications where the weight of an item is very important resistivity density products are more important than absolute low resistivity – it is often possible to make the conductor thicker to make up for a higher resistivity; and then a low resistivity density product material (or equivalently a high conductance to density ratio) is desirable. For example, for long distanceoverhead power lines, aluminium is frequently used rather than copper because it is lighter for the same conductance.

Material	Resistivity (nΩ·m)	Density (g/cm3)	Resistivity-density product (nΩ·m·g/cm3)
Sodium натрий	47.7	0.97	46
Lithium литий	92.8	0.53	49
Calcium кальций	33.6	1.55	52
Potassium калий	72.0	0.89	64
Beryllium бериллий	35.6	1.85	66
Aluminium алюминий	26.50	2.70	72
Magnesium магний	43.90	1.74	76.3
Copper медь	16.78	8.96	150
Silver серебро	15.87	10.49	166
Gold золото	22.14	19.30	427
Iron железо	96.1	7.874	757

Silver, although it is the least resistive metal known, has a high density and does poorly by this measure. Calcium and the alkali metals have the best resistivity-density products, but are rarely used for conductors due to their high reactivity with water and oxygen. Aluminium is far more stable. Two other important attributes, price and toxicity, exclude the (otherwise) best choice: Beryllium. Thus, aluminium is usually the metal of choice when the weight of some required conduction (and/or the cost of conduction) is the driving consideration.