pebble vs scoria

pebble

noun
  • A form of slow-burning gunpowder in large cubical grains. 

  • A particle from 4 to 64 mm in diameter, following the Wentworth scale. 

  • Transparent and colourless rock crystal. 

  • A small stone, especially one rounded by the action of water. 

  • A small droplet of water intentionally sprayed on the ice that cause irregularities on the surface. 

verb
  • To pave with pebbles. 

  • To place a pebble at (a vertex of a graph) according to certain rules; see pebble game. 

  • To deposit water droplets on the ice. 

  • To give (leather) a rough appearance with small rounded prominences. 

scoria

noun
  • The slag or dross that remains after the smelting of metal from an ore. 

  • Rough masses of rock formed by solidified lava, and which can be found around a volcano's crater. 

How often have the words pebble and scoria occurred in a corpus of books? (source: Google Ngram Viewer )