Ferruginous Quartz: Red Quartz, Properties, Types, Occurrence

Ferruginous Quartz, also known as red quartz, is a variety of quartz that is colored red by the presence of iron oxide. The iron oxide can be in the form of hematite, goethite, or limonite. Ferruginous Quartz is typically opaque, but it can sometimes be translucent or even transparent. It is often called "hematoid quartz".

Ferruginous Red Quartz often forms in hydrothermal veins, areas where mineral-rich fluids flowed and deposited crystals. It can also be found in sedimentary rocks near iron ore deposits or in weathered zones where iron minerals oxidize.

Ferruginous Quartz - Red Quartz

Ferruginous Quartz is usually massive and opaque, and can be found in a variety of geological settings, including sandstone, shale, and quartzite. Ferruginous quartz is often found in association with other iron-rich minerals, such as magnetite, hematite, and limonite. It can also be found in association with other types of quartz, such as agate and jasper.

Natural 'eisenkiesel' quartz cluster.
Chella, Valencia, Valencian Community, Spain
Photo: Carlos Pareja

Ferruginous Quartz Properties

Composition: Silicon dioxide (SiO₂) with inclusions of iron oxides, primarily hematite and limonite.

Color: Varies depending on the type and concentration of iron oxide inclusions. Can range from:

Yellow: Pale to golden.
Orange: Pinkish-orange to deep reddish-orange.
Red: Brick red to brownish-red to fiery crimson.
Brown: Yellowish-brown to dark reddish-brown.

Luster: Vitreous (glassy shine).

Crystal System: Trigonal.

Streak: White, similar to regular quartz.

Hardness: 7 on the Mohs scale, similar to regular quartz, making it a relatively hard and durable stone.

Cleavage: None, does not cleave easily.

Crystal Form: Can occur in well-defined, prismatic crystals with pyramid terminations, often in clusters or druses. Can also be massive or botryoidal (rounded grape-like clusters).

Density: 2.65 g/cm³, slightly denser than regular quartz due to the heavier iron oxide inclusions.

Transparency: Can range from transparent to translucent, depending on the density and distribution of inclusions.

Fracture: Conchoidal, breaks with smooth, curved surfaces.

Solubility: Insoluble in most common solvents, but will dissolve in hydrofluoric acid.

Magnetism: Non-magnetic, does not attract or repel magnets.

Fluorescence: May fluoresce weakly under long-wave ultraviolet light, depending on the type and concentration of iron oxide inclusions.

Pleochroism: Very weak, may show slight variations in color depending on the viewing angle.

Refractive Index: 1.544-1.553, slightly higher than regular quartz due to the higher density of the inclusions.

Ferruginous Quartz
Photo: Sandro Bonfiglio

Ferruginous Red Quartz Occurrence

Ferruginous Red Quartz, captivating with its fiery hues and intriguing formations, can be found in various locations around the globe. Here's a rundown of some prominent sources:

Brazil: A hotspot for diverse types, including the intense Fire Quartz from Minas Gerais state and the vibrant Tangerine Quartz from Bahia.

Madagascar: Renowned for its clear varieties with red inclusions, offering stunning contrast and sparkle.

India: Telangana state features deep red Eisenkiesel Quartz, while the Himalayas yield diverse colors and patterns.

Morocco: Known for its unique Jacinto de Compostela variety, small double-terminated crystals with rich red-brown hues.

Germany: The namesake Eisenkiesel Quartz originates here, typically showing a uniform red color and good translucency.

Ferruginous Quartz - Eisenkiesel
Credit: Crystalclassics_co_uk

Ferruginous Quartz Types

Fire Quartz

Fire Quartz: This variety boasts a vibrant, fiery red color due to the presence of hematite. It's often translucent, allowing light to play through the inclusions, creating a mesmerizing effect. Fire quartz is found in various locations, including Brazil, Madagascar, and India.

Tangerine Quartz

Tangerine Quartz: This orange-hued variety is named for its resemblance to the citrus fruit. It's typically translucent and can sometimes exhibit chatoyance, a shimmering effect caused by light interacting with the internal fibers. Tangerine quartz is most commonly found in Madagascar and Namibia.

Eisenkiesel Quartz

Eisenkiesel Quartz: This German term translates to "iron pebble" and refers to a type of ferruginous quartz with an even, deep red-brown color. It's usually opaque and massive, meaning it doesn't form well-defined crystals. Eisenkiesel quartz is primarily found in Spain and Portugal. Eisenkiesel (German for "iron pebble", pronounced "i-zen-keezle").

Jacinto de Compostela

Jacintos de Compostela: These are small, translucent red-brown crystals known for their clustered, hedgehog-like formations. Jacinto quartz is typically opaque, but it can sometimes be translucent. They're found in Spain, specifically near the city of Compostela, and are considered collectors' items.

Bright red hematite phantom quartz cluster, from Orange River, South Africa.
Photo: The Eclectic Collects

Ferruginous Red Quartz Uses

Ferruginous Red Quartz, with its fiery color and mesmerizing inclusions, offers a variety of uses beyond simply being admired for its beauty.

Practical Uses:

Jewelry: The striking red hues and intriguing patterns make Ferruginous Red Quartz a popular choice for jewelry makers. Its hardness and durability allow it to be cut and polished into stunning rings, pendants, bracelets, and earrings.

Decorative Stones: The unique appearance and captivating energy of this stone make it a sought-after addition to collections and home decor. It can be displayed individually, grouped with other crystals, or even incorporated into sculptures or artistic pieces.

Gemstone Carvings: Skilled artisans sometimes carve intricate designs or figures into Ferruginous Red Quartz, taking advantage of the variations in color and inclusions to create one-of-a-kind artworks.

Quartz Var Eisenkies
Photo: Sandro Bonfiglio

Metaphysical Uses:

Crystal Healing: In crystal healing practices, Ferruginous Red Quartz is believed to hold various beneficial properties. Some common uses include:

Stimulating vitality and passion: The fiery red color is associated with life force, energy, and enthusiasm. It's considered a stone of empowerment and can help reignite passion and purpose.

Grounding and stabilizing: Despite its energetic nature, the iron oxides within the quartz are believed to provide grounding and stability, balancing out the fiery energy.

Boosting courage and overcoming fears: The vibrant red is associated with confidence and bravery, and the stone is believed to help individuals face challenges and overcome fears.