Authorities said the unique pieces taken would be easily identified, which could make it difficult for the robbers to sell them.
"It is uncommon for most citizens to possess such minerals," the CHP said in a statement.
It was the second heist this year of rare, valuable metals in Northern California. In February, thieves made off with large chunks of gold that were on display in a Siskiyou County courthouse.
Investigators were trying to determine if there is a connection between the two heists.
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