un ting ▁to ▁initi ate ▁crack ing , ▁re le asing ▁the ▁internal ▁energy ▁and ▁sh atter ing ▁the ▁glass . ▁However , ▁nin ja ▁rocks ▁are ▁in effect ive ▁if ▁the ▁sh ards ▁are ▁ins u fficient ly ▁sharp , ▁thrown ▁with ▁too ▁little ▁energy , ▁or ▁thrown ▁against ▁wind sh ield s , ▁as ▁these ▁are ▁made ▁of ▁a ▁l amin ated ▁type ▁of ▁safety ▁glass , ▁and ▁therefore ▁do ▁not ▁sh atter . ▁ ▁Leg al ▁status ▁ ▁United ▁States ▁Of ▁America ▁ ▁California ▁In ▁California , ▁since ▁ 2 0 0 3 , ▁nin ja ▁rocks ▁are ▁explicitly ▁listed ▁as ▁burg l ary ▁tools , ▁and ▁their ▁possession ▁with ▁intent ▁to ▁burg lar ize ▁is ▁a ▁mis de mean or ▁pun ish able ▁by ▁up ▁to ▁six ▁months ▁in ▁county ▁j ail ▁and / or ▁a ▁fine ▁of ▁up ▁to ▁$ 1 0 0 0 . ▁Leg al ▁records ▁do ▁not ▁use ▁the ▁phrase ▁" n in ja ▁rocks ", ▁prefer ring ▁more ▁precise ▁phr ases ▁such ▁as ▁" cer am ic ▁or ▁por cel ain ▁spark ▁plug ▁ch ips ▁or ▁pieces ". ▁ ▁Until ▁ 2 0 0 3 , ▁" burg l ary ▁tools " ▁in ▁California ▁did ▁not ▁include ▁devices ▁to ▁break ▁glass . ▁In ▁late ▁ 2 0 0 1 , ▁two ▁important ▁conv ict ions ▁including ▁possession ▁of ▁nin ja ▁rocks ▁were ▁appe aled . ▁In ▁People ▁v . ▁Gordon ▁( 2 0 0 1 ) ▁ 9 0 ▁Cal . App . 4