amorphous Simulant jet simulant

French Jet (Black Glass)

Formula Soda-lime or lead glass; coloured black with iron oxide, manganese oxide, or carbon black; may be lead-rich for higher density and lustre

Crystal Structure

CDL Notation

 #! Species: French Jet (black glass; jet simulant)
#! System: Amorphous (glass)
#! Habit: Moulded/faceted black glass
amorphous[glassy]:{massive}

Crystal System amorphous

Point Group none

Crystal Forms (1)

{massive}

Quick Facts

Hardness

5.0

Specific Gravity

2.4

Refractive Index

1.48

Optical Character

Isotropic

Physical Properties

Crystal System: amorphous
Hardness (Mohs): 5.0
Specific Gravity: 2.4
Cleavage: None
Fracture: Conchoidal
Lustre: Vitreous to brilliant

Optical Properties

Refractive Index: 1.48
Birefringence: 0
Optical Character: Isotropic
Fluorescence: Variable

Origin & Identification

Origin: Simulant
First Produced: 1800
Diagnostic Features: High SG 2.40-3.50 vs jet 1.30-1.35 (definitive hydrostatic test); cold to touch (glass thermal conductivity); conchoidal fracture; no smell on hot-point; harder than jet; possible gas bubbles under magnification; no organic microstructure (jet shows wood-grain)

Characteristics

Colours

Uniform black (no brown tinge unlike vulcanite)

Common Inclusions

Possible gas bubbles; conchoidal fracture on broken edges

Notes

Black glass jet simulant; popular 1840s-1900s for Victorian mourning jewellery. "French jet" is primarily Bohemian and French glass industry production, not only French. Key diagnostic: high SG 2.40-3.50 (jet = 1.30-1.35; French jet sinks rapidly in liquids that float jet). Cold to touch (glass has high thermal conductivity). Conchoidal fracture on broken edges. No smell on hot-point (vs jet = aromatic coal; vulcanite = sulfur/rubber). Harder than jet (H 5-5.5 vs jet 2.5-4). Dictionary of Gems and Gemology (Springer) (DOI 10.1007/978-3-540-72816-0_8882) [PARTIALLY_SUPPORTED — catalogue record only]. Read 7th ed. p.330 (DOI 10.4324/9780080507224) [PARTIALLY_SUPPORTED]. VERIFIED.md status [PARTIALLY_SUPPORTED] per S-014. Included as curriculum-standard simulant.