The fruit was expensive, being imported.

[diamondcutter]

1a. Used economically, one tin will last for six weeks.
=1b. If it is used economically, one tin will last for six weeks.
Source: Practical English Usage, Michael Swan, OUP

2a. The fruit was expensive, being imported.
= 2b. The fruit was expensive because it was imported.
Source: Advanced Grammar in Use, Martin Hewings, CUP

Both the original subordinate clauses use the passive voice, but I don’t understand when simplified why 1a uses “used”--the basic form of the past participle while 2a uses “being imported” --I don’t know whether it’s the progressive aspect of the past participle or the passive form of the present participle. Could you please enlighten me?

 

[jutfrank]

I'm not quite sure what you're asking.

The word being is in present participle form and the word imported is in past participle form. The two words comprise a participle clause in the passive voice.