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Gabbro, Diabase, Basalt

LINK TO THE FREE ROCK IMAGE ID KEY: https://rockpapa.github.io/Rock-Image... In this video, we take a close look at three closely related igneous rocks: Gabbro • Diabase • Basalt These rocks are all mafic, meaning they are rich in iron, magnesium, and calcium, low in quartz, and derived directly from mantle magma. Although they contain the same minerals, they look different because they cool in different places and at different rates. In this episode, we cover: • What “mafic” means and how it differs from felsic rocks • The shared mineral makeup of gabbro, diabase, and basalt – Pyroxene (black mineral) – Calcium-rich feldspar (white mineral) – Minor hornblende and olivine in some cases • How to use simple clues like crystal size and shape to tell these rocks apart • Why pyroxene and hornblende cannot be scratched by a nickel • Why calcium-rich feldspar crystals often look rod-shaped or stringy instead of blobby We then look at how and where each rock forms: ✅ Gabbro Forms deep underground where magma cools very slowly, allowing large crystals to grow. ✅ Diabase Forms in dikes and sills close to the surface. It cools faster than gabbro, producing small but visible crystals. ✅ Basalt Erupts at the surface as lava and cools very quickly, producing tiny or invisible crystals. Vesicular basalt forms when gas bubbles are trapped during cooling. We also explore how these three rocks fit into the structure of oceanic crust: • Gabbro at the base • A sheeted dike complex made of diabase • Basalt lava (often pillow basalt) at the top Finally, we discuss how ocean crust can be pushed up onto land during continental collisions, allowing us to see these rocks exposed at the surface today. This video is designed for rockhounds, students, hikers, and anyone who wants a clear, practical way to identify mafic igneous rocks in the field.