Powellite Mineral Overview

• Mineral name: Powellite
• Mineral class: Molybdate (oxide group)
• Chemical formula: CaMoO₄ (calcium molybdate)
• Crystal system: Tetragonal
• Mohs hardness: 3.5–4
• Color range: Colorless, white, yellow, brown, blue-green
• Luster: Adamantine to resinous
• Streak: White
• Cleavage: Distinct
• Fracture: Conchoidal to uneven
• Specific gravity: Approximately 4.2–4.4
• Transparency: Transparent to translucent
• Common locations: United States, Mexico, Russia, Chile
• Uses: Minor molybdenum ore, collector mineral
• Similar minerals: Scheelite, wulfenite

Naming and Classification

Powellite is a calcium molybdate mineral, named after American geologist John Wesley Powell.

It belongs to the molybdate subgroup of oxide minerals, closely related to:

• Scheelite (CaWO₄) (tungstate analogue)

These minerals share similar structures and often occur in similar geological environments.

Physical and Optical Characteristics

Powellite typically forms:

• Tetragonal dipyramidal crystals
• Tabular or pyramidal shapes
• Massive or granular aggregates

Crystals can be well-formed but are often small.

Its color varies widely, including:

• Colorless or white
• Yellow to golden
• Brownish or bluish-green tones

The luster is often adamantine, giving it a bright, almost diamond-like shine.

With a Mohs hardness of 3.5 to 4, powellite is relatively soft.

Fluorescence (Key Feature)

One of the most notable properties of powellite:

• Strong fluorescence under UV light
• Typically glows yellow, white, or bluish-white

This makes it popular among collectors who use UV lighting.

Chemical Composition and Structure

Powellite is composed of:

• Calcium (Ca)
• Molybdenum (Mo)
• Oxygen (O)

Its structure is similar to scheelite, with:

• Tetrahedral molybdate groups (MoO₄)

This structure contributes to its optical and fluorescent properties.

Formation and Geological Occurrence

Powellite forms in hydrothermal and contact metamorphic environments, particularly in:

Skarn Deposits

• Formed where magma interacts with carbonate rocks

Hydrothermal Veins

• Deposited from mineral-rich fluids

Typical formation conditions include:

• Moderate to high temperatures
• Molybdenum-rich fluids

It is commonly associated with:

• Scheelite
• Quartz
• Calcite
• Molybdenite

Common Locations

Powellite is found in several regions:

• United States: California, Arizona, Nevada
• Mexico: Notable crystal specimens
• Russia and Chile: Additional deposits

U.S. localities are especially known for fluorescent specimens.

Uses and Practical Significance

Powellite has limited but notable uses:

Minor Ore of Molybdenum

• Occasionally contributes to molybdenum extraction

Collector Mineral

• Valued for:
  • Crystal form
  • Fluorescence

It is not a primary industrial source compared to molybdenite.

Similar and Related Minerals

Powellite can resemble:

• Scheelite: Often harder and associated with tungsten
• Wulfenite: Typically orange-red and more tabular
• Calcite: Softer and reacts with acid

Fluorescence and chemical testing help distinguish powellite.

Identification Notes for Collectors

• Look for pale-colored tetragonal crystals
• Test for UV fluorescence (strong indicator)
• Note moderate softness (3.5–4)
• Observe adamantine luster
• Consider association with molybdenum or skarn deposits

Powellite is a calcium molybdate mineral, recognized for its bright luster and strong fluorescence, making it a visually appealing and scientifically interesting specimen for collectors.