7. Income Tax (Details 1) (USD $)	3 Months Ended		6 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Tax Details 1
Federal tax at statutory rate	$ 478,000	$ 555,000	$ 891,000	$ 847,000
State taxes, net of federal benefit	14,000	23,000	26,000	32,000
Excess percentage depletion	(200,000)	(175,000)	(403,000)	(310,000)
Other adjustments, net	1,000	2,000	(4,000)	4,000
Income tax expense	$ 293,000	$ 405,000	$ 510,000	$ 573,000
Effective rate expressed as a percentage of income before income tax	20.80%	24.90%	19.50%	23.00%