Augmented Reality (AR) and Virtual Reality (VR) platforms now support shared, immersive experiences that enable people to directly physically and perceptually engage with mathematical objects, including shared objects. These new forms of AR/VR technology -- which we call "shared holographic AR/VR" (shAR) -- enable multiple learners to manipulate and reason about the same mathematical objects represented as holograms projected in a joint three-dimensional collaborative space in front of them, using intuitive hand gestures. This Interactive Tools and Demos paper discusses an AR/VR environment for collaboratively exploring geometry conjectures about shapes and solids. We show data of learners collaborating in our environment using speech, dynamic actions on virtual objects, and hand gestures. We discuss the potential of AR and VR environments for mathematics learning.