While we're on the subject of zombies, I'd like to shift our attention to so-called "zombie volcanoes"—those older than 12,000 years old but younger than 2.6 million years. They're called "zombies" because they haven't erupted for that length of time but still show seismicity, gas emissions, or deformation. They are technically dormant but not extinct. One such zombie volcano is situated in Bolivia & called Uturuncu, the tallest mountain in Bolivia, standing 3.7 miles high, or 19,711 ft (6,008 m). It hasn't erupted in 250,000 years but is showing active volcano-like behavior because magma, gases, & briny fluids are circulating through a huge hydrothermal system.

3 mountains in the world come fairly close to having distinct colors of the rainbow, though none of them contain all the colors of the rainbow, nor all 7 colors of the rainbow. The Rainbow Mountain in China contains red, orange, yellow & green, but blue, indigo & violet are not present. It was formed over millions of years through sediment deposition, tectonic uplift, and erosion. Layers of sandstone & other minerals were laid down horizontally, then later tilted & exposed as tectonic plates pushed upward. Wind & water erosion gradually carved the dramatic ridges & cliffs, revealing the stacked mineral layers as vivid stripes.

The second rainbow mountain is located in Peru, and its colors are red, pink, yellow, green, white & brown. Vinicunca's colors come from layered sedimentary rocks. Ancient rivers, lakes, & shallow deposits were laid down millions of years ago, such as iron-rich clays, quartz sands, carbonates, and marls, which are sedimentary rocks made of a mix of calcium carbonate & fine-grained clay & silt. When the Andes uplifted, the layers were tilted & fractured, exposing a cross-section of the mineral bands. Its colors are red, pink, yellow, green, white & brown. It has more distinct hues than China.

Bought this little box of thin sections at a local antique store. It likely isn’t that old probably 1970s - 80s at most. Took a couple pictures of the prettier slides

IGNEOUS PETROLOGY: MAFIC ROCKS (45–52% SIO2)

INTRODUCTION

Igneous petrology is the scientific study of rocks formed through the solidification of magma or lava.

Within this branch of geology, mafic rocks represent an essential group because they are among the most abundant rocks on Earth and are fundamental to the formation of oceanic crust and volcanic landforms.

Mafic rocks are defined as igneous rocks with silica contents between 45% and 52%.

They are enriched in magnesium and iron (the word mafic comes from "magnesium" and "ferric") and have relatively low amounts of silica compared to intermediate and felsic rocks.

Their chemical and mineralogical properties give them distinctive textures, colors, and field occurrences.

BASIC CHARACTERISTICS OF MAFIC ROCKS

Mafic rocks are typically dark-colored (black to dark gray) due to the dominance of ferromagnesian minerals.

They are denser than felsic and intermediate rocks but less dense than ultramafic rocks.

Common minerals in mafic rocks include plagioclase feldspar (calcium-rich varieties), pyroxene, and olivine, with minor amounts of amphibole. Quartz is usually absent or very rare.

The typical silica range of 45–52% gives these rocks a balance between high-temperature and moderate-temperature mineral assemblages, making them stable in a variety of tectonic environments.

CLASSIFICATION OF MAFIC ROCKS

Mafic rocks can be grouped into two major categories based on their environment of formation:

Plutonic (intrusive) mafic rocks:

These form when magma cools slowly beneath the Earth’s surface, allowing coarse crystals to grow.

The most common example is gabbro.

Volcanic (extrusive) mafic rocks:

These form when magma erupts and cools rapidly on or near the surface.

Basalt is the most common volcanic mafic rock and is the most abundant volcanic rock on Earth.