ForMatter/Materials/gemstone/Amethyst
mat_gem_quartz_amethyst

Amethyst

quartz (SiO₂) iron-colored + irradiation, purple · purple quartz, amethystine quartz
highlast updated 2026-04-27
metallic 0.00
hue shift +0°

Quartz colored violet to deep purple by iron impurities and natural ionizing radiation acting together. Once a stone of cardinals and popes when Brazilian deposits hadn't yet been opened, now an inexpensive everyday stone — the price collapsed in the 19th century when Minas Gerais came online. Heat-conversion turns amethyst into citrine; many "citrines" on the market are heat-converted amethyst.

SiO₂ in trigonal crystal system (low quartz), Mohs 7. Color from Fe³⁺ + interstitial Fe⁴⁺ centers stabilized by natural γ-irradiation; heating above 300 °C converts to yellow citrine, above 450 °C bleaches color. Specific gravity 2.65. Refractive indices 1.544 / 1.553. Hard enough for daily-wear jewelry but softer than topaz or beryl.

mechanical

  • mohs_hardness7
  • specific_gravity2.65
source: GIA Amethyst Quality Factors

optical

  • refractive_index_omega1.544
  • refractive_index_epsilon1.553
source: GIA

Sustainability

  • embodied carbon kg co2e per carat0.4
  • recyclabilityhigh
  • biodegradableFalse
  • localityprimary mining: Brazil (Minas Gerais), Uruguay, Zambia, Madagascar, Russia (Siberia, historical)
visual
violet to deep purple, often with subtle color zoning visible under magnification

PBR starter values

Principled BSDF defaults derived from the sphere crystalline finish. Reasonable seed for Blender, Substance, Keyshot, Rhino — tune per material.

# finish:      crystalline
albedo        #8a4ec0
metallic      0.00
roughness     0.05
ior           2.42
transmission  1.00
clearcoat     0.00
sheen         0.00
anisotropic   0.00
copy as JSON 
{
  "albedo": "#8a4ec0",
  "metallic": 0.0,
  "roughness": 0.05,
  "ior": 2.42,
  "transmission": 1.0,
  "clearcoat": 0.0,
  "sheen": 0.0,
  "anisotropic": 0.0
}
Blender 4.x Python 
# Blender 4.x — Principled BSDF
# Amethyst · finish: crystalline
import bpy
mat = bpy.data.materials.new(name="mat_gem_quartz_amethyst")
mat.use_nodes = True
bsdf = mat.node_tree.nodes["Principled BSDF"]
bsdf.inputs["Base Color"].default_value         = (0.2542, 0.0762, 0.5271, 1.0)
bsdf.inputs["Metallic"].default_value           = 0.000
bsdf.inputs["Roughness"].default_value          = 0.050
bsdf.inputs["IOR"].default_value                = 2.420
bsdf.inputs["Transmission Weight"].default_value = 1.000
bsdf.inputs["Coat Weight"].default_value        = 0.000
bsdf.inputs["Sheen Weight"].default_value       = 0.000
bsdf.inputs["Anisotropic"].default_value        = 0.000
KeyShot Python (lux) 
# KeyShot 11+ — lux Python API, Generic material
# Amethyst · finish: crystalline
# Run from Window → Scripting Console
import lux
mat = lux.createMaterial(name="mat_gem_quartz_amethyst", materialType="Generic")
mat.setProperty("diffuse",      (138, 78, 192))   # 8-bit sRGB
mat.setProperty("metallic",     0.000)
mat.setProperty("roughness",    0.050)
mat.setProperty("indexOfRefraction", 2.420)
mat.setProperty("transparency", 1.000)
mat.setProperty("coatingWeight", 0.000)
Substance pbrMetalRough 
{
  "_format": "Substance Designer / Painter \u2014 pbrMetalRough constants",
  "_about": "Amethyst \u00b7 finish: crystalline",
  "baseColor": {
    "r": 0.2542,
    "g": 0.0762,
    "b": 0.5271
  },
  "metallic": 0.0,
  "roughness": 0.05,
  "ior": 2.42,
  "opacity": 0.0,
  "anisotropyLevel": 0.0,
  "_notes": "Channels listed are the standard Substance pbrMetalRough output. Drop into a Uniform Color node per channel, or as the constant input on a layered stack."
}
glTF 2.0 Metallic-Roughness 
{
  "asset": {
    "version": "2.0",
    "generator": "ForMatter"
  },
  "materials": [
    {
      "name": "mat_gem_quartz_amethyst",
      "pbrMetallicRoughness": {
        "baseColorFactor": [
          0.2542,
          0.0762,
          0.5271,
          1.0
        ],
        "metallicFactor": 0.0,
        "roughnessFactor": 0.05
      },
      "extensions": {
        "KHR_materials_ior": {
          "ior": 2.42
        },
        "KHR_materials_transmission": {
          "transmissionFactor": 1.0
        }
      }
    }
  ]
}
USD Preview Surface 
# USD Preview Surface — UsdShade.MaterialLook prim attributes
# Amethyst · finish: crystalline
def Material "mat_gem_quartz_amethyst" {
    token outputs:surface.connect = </mat_gem_quartz_amethyst/PreviewSurface.outputs:surface>

    def Shader "PreviewSurface" {
        uniform token info:id = "UsdPreviewSurface"
        color3f inputs:diffuseColor = (0.2542, 0.0762, 0.5271)
        float   inputs:metallic     = 0.000
        float   inputs:roughness    = 0.050
        float   inputs:ior          = 2.420
        float   inputs:opacity      = 0.000
        float   inputs:clearcoat    = 0.000
        token   outputs:surface
    }
}
↓ download glTF material
Substitutes
Citrine
Smoky Quartz
Rose Quartz

Citations