It is an image of stylized atom. There is a small concentric circle in the middle that isn't touched by anything. Three elongated ovals form the outside, one which stands vertically and the other two form an X.
This is a Physics icon. We've made it in iOS style
, first introduced in iOS version 7 and supported in all later releases up until now (at least iOS 11). This style is based on thin two-pixel lines and is optimized for 50x50 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 13,700 icons, all in the same style and quality.