This paper presents the Ruskin Rocks project which is developing a rock instrument, making use of interactive multimedia to augment the musical characteristics of stones. Several historical rock instruments, which inspired the building of this instrument - iRock - are discussed. Fundamental vibration theory is applied to understand the musical nature of the rocks, and empirical data presented to support the decisions made for the instrument design. Several new concepts based on user-centred design have been introduced to study the effects of interfaces and interactivities. The paper also outlines the iRock system architecture and discusses augmentations to the instrument and signal processing techniques.