Lithium
This is the lightest (specific gravity 0.54) and hardest metal in this group. It is stored in mineral oil or inert gases.
Lithium contributes to improving the quality characteristics of metals, is used in various alloys (for example, anti-friction alloys). Due to its high affinity for other elements it is used, inter alia, for obtaining other metals in pure form
Source: "Explanations to the Harmonized System of Foreign Economic Activity of the Russian Federation (HS FED Russia)" (prepared by the State Customs Committee of the Russian Federation) (volume 1, sections I - VI, groups 1 - 29)