Hash won't work in option_from_collection_for_select

structure.html.erb

<%= form_for(@structure) do |f| %>
  <%= f.select :structural_material, options_from_collection_for_select(@materials, :material, :material), :prompt => "Select" %>
<% end %>

structure.rb

class Structure < ActiveRecord::Base
  
  validates :year_home_built, :presence => true
  validates :year_home_purchased, :presence => true
  validates :structural_material, :presence => true
  validates :roof_style, :presence => true
  validates :reconstruction_cost, :presence => true
  
  @@materials_list = [{
      material: 'Brick'
    },
    {
      material: 'Hardiplank'
    },
    {
      material: 'Stone'
    },
    {
      material: 'Stucco'
    },
    {
      material: 'Vinyl'
    },
    {
      material: 'Wood'
    }]

  def self.fetch_materials
    @@materials_list
  end

end

structures_controller.rb

class StructuresController < ApplicationController
  # GET /structures/new
  # GET /structures/new.json
  def new
    @structure = Structure.new
    
    @materials = Structure.fetch_materials
    
    logger.debug @materials

    respond_to do |format|
      format.html # new.html.erb
      format.json { render json: @structure }
    end
  end

end

I can get this working if I use only an array and option_for_select, just not options_from_collection_for_select with a hash.

Thanks to @mikelikesbikes, my answer was to use OpenStruct objects instead of standard Hashes.