けど usage in ”魔石灯”がいい例だけど、”魔石”は…


I know that けど is a colloquial form of けれども and that is used to connect two
sentences with the meaning of "but, although" but in the following sentence I
cannot understand its usage.

> 僕達のホームにあった”魔石灯”がいい例だ **けど**
> 、”魔石”はヒューマンの技術で加工することで色々な方面―発火装置だとか、食糧を保存する冷凍器とか―に活用できるから、貴重な資源扱いになっている

The following sentence is my translation:

> The "magic stone" is used as a valuable resource, because it can be used in
> different fields, such as in incendiary devices, in the freezers to store
> the food of first necessity and a good example is the "light at the magic
> stone" that we had at our home.

In this sentence is it used with a different nuance?




This is an example of another important role of けど, けれど, が, だが, ですが, etc: to
provide introductory, background information (前置き) before dealing with the
main issue (本題). Any monolingual dictionary explains this usage.

[From デジタル大辞泉](http://dictionary.goo.ne.jp/jn/68969/meaning/m0u/):

> ２ **ある事実を前置きとして述べ、本題に結びつける**
> 意を表す。「経験から言うんだ―、時間には厳しいほうがいい」「これおもしろい本だ―、君読まないか」

Examples:

>   * 今日は日曜日だけど、どこに行きたい？ It's Sunday, (so) where do you want to go?
>   * この前の話だけど、覚えてる？ Do you remember it, what we discussed the other day?
>   * 去年日本に行ったんだけど、楽しかったよ。 I visited Japan last year, and it was fun.
>

Some of these can be safely translated using _but_ (eg 失礼ですけど = "Excuse me but
..."). In your case, you can simply translate it as if it were two separate
sentences: "... is a good example. The magic stone is used as ..."

