How to identify Druzy Quartz with Goethite

To correctly identify Druzy Quartz with Goethite (SiO2 (Quartz) with FeO(OH) (Goethite)), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.

Step-by-step identification

1. 1

   Color

   Overall color and any zoning or banding

   Typically yellow, orange, brown, reddish-brown, or sometimes iridescent due to goethite inclusions or coatings. The quartz itself is colorless to white.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) for the quartz crystals, often with a sub-metallic to earthy luster for the goethite. The overall appearance is sparkling due to the druzy quartz.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Rough, granular, or sugary due to the multitude of small, interlocking quartz crystals. The goethite may appear as fine dust, needle-like inclusions, or botryoidal growths.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Microcrystalline quartz crystals forming a druzy layer, often with individual crystals exhibiting hexagonal prism and pyramid forms. Goethite can be acicular, fibrous, botryoidal, or massive.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz: None. Goethite: Perfect on {010}, but rarely observed in microcrystalline or included forms.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, vugs, geodes, and fracture fillings in various host rocks, including igneous, metamorphic, and sedimentary formations. Often found in areas with iron-rich groundwater or near oxidized iron ore deposits.

Key Facts

Hardness

Quartz: 7 on the Mohs scale. Goethite: 5-5.5 on the Mohs scale. The overall hardness will be dominated by quartz.

Specific Gravity

Quartz: 2.65 g/cm³. Goethite: 3.3-4.3 g/cm³. The aggregate specific gravity will vary depending on the proportion of goethite.

Crystal System

Quartz: Trigonal. Goethite: Orthorhombic.

Color

Colorless to white quartz with yellow, orange, brown, reddish-brown, or iridescent goethite.

Luster

Vitreous for quartz, sub-metallic to earthy for goethite.

Transparency

Transparent to translucent for quartz; opaque for goethite.

Fracture

Conchoidal for quartz; uneven to sub-conchoidal for goethite.

Cleavage

Quartz: None. Goethite: Perfect on {010}.

Composition

Silicon dioxide (SiO2) for quartz, and hydrated iron oxide hydroxide (FeO(OH)) for goethite.

Physical characteristics

• Crystal Habit: Druzy (microcrystalline crusts) for quartz; acicular, fibrous, botryoidal, or massive for goethite.
• Cleavage Type: Quartz: Absent. Goethite: Perfect in one direction, but rarely observed in included forms.
• Fracture Type: Conchoidal for quartz; uneven to sub-conchoidal for goethite.
• Tenacity: Brittle for both quartz and goethite.
• Luster Type: Vitreous for quartz; sub-metallic to earthy for goethite.

Explore Druzy Quartz with Goethite