Beryllium

Beryllium is an alkaline earth metal, one of the basic atomic elements and number 4 on the periodic table.

Enterprise detected beryllium on a supposedly haunted planet from orbit in 2151. The Barbara series of Andromedan android had a skeleton of beryllium-titanium alloy. 

The late 24th century Starfleet communicators consisted of several materials, including beryllium. 

In its crystalline form, beryllium is a deep reddish purple color and slightly translucent. In the 2370s, it was the standard currency in Grid 539 of the Delta Quadrant. There, even a small amount of the substance was quite valuable; several species would trade a large fleet of starships for a block of no more than a few cubic centimeters in volume. In mid-2376, Neelix traded Abaddon a few plasma couplings for a number of items including a beryllium crystal, although neither realized the value of the beryllium until Seven of Nine identified it among the otherwise useless trinkets. Neelix offered to return it in exchange for information about another object obtained from Abaddon, a ship called Alice, which had possessed USS Voyager helmsman Tom Paris.