Anthropogenic (Man-made industrial deposit)
Slag (Industrial Byproduct)
Ferro-silicate glass (Slag)
Hardness: 5.5-6.5; Color: Dark brown to black with occasional metallic sheen; Luster: Glassy to dull/earthy; Structure: Amorphous/Vesicular (pitted with air bubbles); Specific Gravity: 2.8-4.0 (often high due to iron content).
- Hardness
- 5
- Color
- Dark brown to black with occasional metallic sheen
- Luster
- Glassy to dull/earthy
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Physical properties
Hardness: 5.5-6.5; Color: Dark brown to black with occasional metallic sheen; Luster: Glassy to dull/earthy; Structure: Amorphous/Vesicular (pitted with air bubbles); Specific Gravity: 2.8-4.0 (often high due to iron content).
Formation & geological history
Formed as a byproduct of smelting ores (such as iron or copper) to separate the desired metal from the unwanted stony impurities. This process involves intense heat and rapid cooling. Age is typically modern/industrial (19th-21st century).
Uses & applications
Used in construction as road base, railroad ballast, or as an aggregate in concrete and asphalt. High-quality colorful glass slag (like Leland Blue) is used for lapidary work and jewelry.
Geological facts
Slag is frequently mistaken for meteorites due to its dark color, heavy weight, and pitted surface. However, the presence of vesicles (gas bubbles) like those seen in this specimen is a hallmark of slag and rarely found in meteorites.
Field identification & locations
Identify in the field by looking for gas bubbles (craters), glassy texture where chipped, and high density. Often found near old railroads, foundries, or steel mills. Collectors often use 'streak tests' to differentiate it from natural ores.
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