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 ~440 °C bleaches the violet (passing through prasiolite green at 420–440 °C), and above ~500 °C converts to yellow citrine; above ~600 °C the stone goes milky from water-bubble Rayleigh scattering. Specific gravity 2.65. Refractive indices 1.544 / 1.553. Hard enough for daily-wear jewelry but softer than topaz or beryl.
Principled BSDF defaults derived from the sphere crystalline finish. Reasonable seed for Blender, Substance, Keyshot, Rhino — tune per material. Or grab the whole library at once: ForMaterials library →
# 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 thickness 0.80 attenuation_distance 1.50
{
"albedo": "#8a4ec0",
"metallic": 0.0,
"roughness": 0.05,
"ior": 2.42,
"transmission": 1.0,
"clearcoat": 0.0,
"sheen": 0.0,
"anisotropic": 0.0,
"thickness": 0.8,
"attenuation_distance": 1.5
}
# 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 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)
{
"_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."
}{
"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 — 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
}
}
GIA quartz-family grading; Brazilian / Uruguayan amethyst-mining literature.
House vocabulary — terms ForMatter uses with intent.
Materials and processes for people who design and make things.
A local-first library of materials, processes, applications, and finishes — equal weight, citable everywhere, with cost-over-volume curves, trade-off profiles, equipment-tier filters, and second-life paths layered onto the data so a student can move from "what is this" toward "what's actually buildable here, now, by me." Part of the renato.design ecosystem — sibling of Plenum, Specimen, Ingenue, gesture, graf, and the Renato Rhino plug-ins. Form and matter, inseparable.
Half of teaching materials is teaching how the material is made into the thing. The standard subscription library was always light on that half. The wedge here isn't better samples or a prettier interface — it's treating Process as a peer entity, not a footnote.
Conway's Material World on raw materials, Lefteri's Making It on processes, Forty's Concrete and Culture, Sparke's Design in Context, Bürdek's Design: History, Theory and Practice of Product Design, Schröpfer's Material Design on materials in architecture, Winchester's The Perfectionists on tolerance, Minshall's Your Life Is Manufactured on the global supply chain, von Busch's Making Trouble on material activism, Were's How Materials Matter, Hegger / Drexler / Zeumer's Basics Materials, Untracht and McCreight on metalsmithing, USDA Forest Products Lab on woods, GIA on gemstones, Schott / CoorsTek / Toray / Owens Corning datasheets, MakeItFrom for verifiable property numbers, ASM Handbook, ISO standards. Museum holdings draw from the Met, MAD, V&A, Smithsonian American Art Museum, Newark Museum of Art, British Museum, Heard Museum, Smithsonian NMAI, Eiteljorg Museum, Philadelphia Museum of Art, Cranbrook Art Museum, and Grand Rapids Art Museum — collection-record permalinks only, designer overview pages and exhibition listings excluded. Voice blocks now ride on every entry kind — material, process, application, and finish — and include Ruskin on iron, Anni Albers on twining, Greg Lynn on the shred-and-teeth NURBS lineage, Pugin on the metal that won't be hammered, Barthes / Yanagi / Benjamin channeled within their philosophy; Sparke, Bürdek, Forty, Conway, Schröpfer, Minshall, von Busch, Lefteri, Pat Pruitt, Mary Lee Hu, Tom Joyce, Albert Paley, and the rest of the contemporary makers quoted verbatim with citation. All cited.
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