PROPERTIES
This property describes whether light can pass through a mineral—ranging from transparent (you can see right through it) to translucent (lets light through, but blurry) to opaque (no light passes through at all).
What is Transparency? (or Diaphaneity)
Metamorphic rocks are formed deep underground when existing rocks are changed by extreme heat and this crushing force.
What is Pressure?
This basic property is usually the first thing you notice when looking at a rock or mineral, but it can be misleading because minerals like quartz come in many different shades (like pink, purple, or clear).
What is Color?
This dark, heavy igneous rock makes up most of the ocean floor and cooled quickly on Earth's surface after erupting from underwater volcanoes.
What is Basalt?
Sedimentary rocks are often easy to spot because they form in visible horizontal layers, which geologists also call by this 6-letter word starting with the letter S.
What are Strata? (or Layers/Bedding)
This special physical property allows certain minerals high in iron—like magnetite—to attract paperclips or stick to iron objects.
What is Magnetism?
When intense pressure squeezes a metamorphic rock, its minerals align into parallel stripes or bands. Rocks with this ribbon-like pattern (like gneiss) are called this.
What is Foliated? (or Foliation)
When a mineral breaks neatly along smooth, flat surfaces or planes, it is showing this property (unlike fracture, which leaves uneven or jagged edges).
What is Cleavage?
Igneous rocks get their name from a Latin word meaning "fire." They form when this liquid rock cools and hardens—called magma when it is underground and this name when it erupts onto Earth's surface.
WHAT IS LAVA
Made from squished layers of fine mud and clay, this very common sedimentary rock splits easily into thin, flat sheets and is often found near rivers and lakes.
What is Shale?
Some minerals have special chemical properties, like calcite. When you drop a weak acid like vinegar onto calcite, it fizzes and produces bubbles of gas due to this specific type of reaction test.
What is the Acid Test? (or Reactivity)
When soft sedimentary limestone is subjected to intense heat and pressure deep inside the Earth, it bakes and transforms into this beautiful metamorphic rock often used for statues and kitchen countertops.
What is Marble?
This term describes how light reflects off the surface of a mineral, and geologists usually classify it as either metallic (shiny like metal) or non-metallic (like glassy, pearly, or dull).
What is Luster?
This lightweight igneous rock is full of tiny air holes, forms from bubbly lava cooling very fast, and is famous for being the only rock that can float on water.
What is Pumice?
This famous geological feature in Arizona was carved out over millions of years by the flowing water of the Colorado River, exposing billions of years of sedimentary rock layers.
What is the Grand Canyon?
This special property describes a mineral's mass divided by its volume (how heavy it feels compared to its size). Geologists often use a related test called "specific gravity" to measure this.
What is Density?
Unlike foliated rocks that have stripes, metamorphic rocks that lack layered bands—like quartzite or marble—are classified by this term meaning "without layers."
What is Non-Foliated?
When testing a mineral, dragging it across an unglazed porcelain plate reveals the color of its powder—a test known by this 6-letter name that is often more reliable than the mineral's surface color.
What is the Streak Test? (or Streak)
When magma cools very slowly deep underground, it forms granite, which has large, visible mineral specks. However, when lava erupts onto Earth's surface and cools super fast, the crystals don't have time to form, giving the rock this type of texture (or look).
What is Fine-Grained? (or Glassy / Smooth)
This organic sedimentary rock, formed from the compressed remains of ancient swamp plants over millions of years, is a major fossil fuel primarily burned to generate electricity.
What is Coal?
When a mineral breaks with rough, jagged, curved, or uneven surfaces—rather than splitting along smooth, flat planes—it exhibits this type of breakage (obsidian breaking with curved edges like glass is a famous example).
What is Fracture?
When the sedimentary rock shale is exposed to heat and pressure, it turns into slate. If you add even more heat and pressure, it eventually transforms into this high-grade metamorphic rock known for its distinct light and dark mineral bands.
What is Gneiss? (pronounced "nice")
Geologists use this numerical scale, rated from 1 to 10, to test a mineral's scratch resistance—where Talc is a soft 1 and Diamond is a hard 10.
What is the Mohs Hardness Scale?
Igneous rocks are divided into two main groups based on where they form. Extrusive rocks form above ground from cooled lava, while this type forms deep inside the Earth from slow-cooling magma.
What are Intrusive Igneous Rocks? (or Plutonic Rocks)
This popular chemical sedimentary rock often forms from ancient sea shells and corals. It easily fizzes and bubbles when you drop vinegar or acid on it because it contains the mineral calcite.
What is Limestone?