We introduce GeaVR, an open-source package containing tools for geological-structural exploration and mapping in Immersive Virtual Reality (VR). GeaVR also makes it possible to carry out quantitative data collection on 3D realistic, referenced and scaled Virtual Reality scenarios. Making use of Immersive Virtual Reality technology through the Unity game engine, GeaVR works with commercially available VR equipment. This allows VR to be accessible to a broad audience, resulting in a revolutionary tool package for Earth Sciences. Users can explore various 3D datasets, spanning from freely available Digital Surface Models and Bathymetric data to ad-hoc 3D high-resolution models from photogrammetry processing. The user can navigate the 3D model in first person, walking or flying above the surrounding environment, mapping the main geological features such as points, lines and polygons, and collecting quantitative data using the provided field survey tools. Such data, including geographic coordinates, can be exported for further spatial analyses. Here we describe three different case studies aimed at showing the potential of our tools. GeaVR is revolutionary as it can be used worldwide, with no spatial limitations, both for geo-education and Earth Science popularization, as well as for research purposes. Secondly, it makes it possible to safely access dangerous areas, such as vertical cliffs or volcanic terrains, virtually from a computer screen or Virtual Reality headset. Furthermore, it can help to reduce carbon emissions by avoiding the use of flights and vehicles to conduct field trips.