Is this safe to assume?
I'm just wondering, is it a true statement to say that you will NEVER see a Spanish that has a 'z' followed by the vowel sounds 'e' and 'i'? I ask this because whenever a verb that ends in a 'z' consonant sound such as 'Empezar' or 'Lanzar' change to 'Empecé' and 'Lancé' in the preterit and to 'Empiece' and 'lance' in the subjunctive. And the same with nouns that end in 'z' consonant sounds such as 'Lápiz' or 'Nariz', to be made plural they are changed to 'Lápices' and 'Narices'. Is it that a 'ze' or 'zi' would sound different than 'ce' or 'ci' or is it that there is just never a time where there IS a 'ze' or 'zi'?
3 Answers
Try to avoid mixing sounds and written conventions because it will only bring confusion upon yourself.
Words ending in z make their plural with c+e :
luz --> luces
haz ---> haces
matiz ---> matices
Some words with e following z.
zeta, zenit, zedilla, zeda, zepelín, neozelandés, Nueva Zelandia.
Some words with i following z.
zinc, zigurat, zíngaro, zigzag.
My teacher had this stupid-sounding little rhyme to help remember this, but it actually helped! "To make it a plural, you don't have to guess, change the z to a c and add es."
Hope that helps, 'cause it's still stuck in my head! 
K
The only thing is that those words appear to be words that are cognates of words from other languages and don't seem to be Spanish words or words derived from Latin, themselves.
(Thank you, by the way)
