From BiblePortal Wikipedia

King James Dictionary [1]

Thine, pronominal adj. Thy belonging to thee relating to thee being the property of thee. It was formerly used for thy, before a vowel.

Then thou mightest eat grapes thy fill, at thine own pleasure.  Deuteronomy 32

But in common usage, thy is now used before a vowel in all cases.

The principal use of thine now is when a verb is interposed between this word and the noun to which it refers. I will not take any thing that is thine. Thine is the kingdom, and the power, and the glory.

In the following passage, thine is used as a substitute for thy righteousness.

I will make mention of thy righteousness, even of thine only.  Psalms 71

In some cases, it is preceded by the sign of the possessive case, like nouns, and is then also to be considered as a substitute.

If any of thine be driven out to the utmost parts of heaven--  Deuteronomy 30

It is to be observed that thine, like thou, is used only in the solemn style. In familiar and common language, your and yours are always used in the singular number as well as the plural.

Webster's Dictionary [2]

(pron. & a.) A form of the possessive case of the pronoun thou, now superseded in common discourse by your, the possessive of you, but maintaining a place in solemn discourse, in poetry, and in the usual language of the Friends, or Quakers.